View Full Version : Bolt life question.
sinlessorrow
06-04-12, 12:24
Hey guys I have a question on bolts. I read the BCG PiP for the M4 has been cancelled because none of the entrants offered any improvements, so this got me curious about why they did not offer any extended life and why bolts seem to break so early.
I did some searching but could not find anything pertaining to my question.
From what I have read the AR-15 bolt in an M4 under heavy firing schedules is generally good for 6-10,000 rounds, while bolts on piston guns seem to be good for 20,000 or so.
Im wondering what makes the difference? The bolt even in piston AR-15's seems to be made the exact same way as the standard bolt, but they seem to last longer.
Is this a material difference, the heat generated from the DI system or is it a little bit of both?
Where did you get your numbers? Especially those that relate to piston guns?
I will say this. In my experience unless someone starts with a virgin gun, there is no way to predict bolt life. Did they start with virgin guns when they did these tests?
Were the weapons properly lubed? What was the firing schedule?
The reason I ask is because I have at least one bolt right now that has over 7.5K rounds through it, many of those are suppressed and yet it seems to be fine. As a matter of fact I have only changed the ejector spring.
Hey guys I have a question on bolts. I read the BCG PiP for the M4 has been cancelled because none of the entrants offered any improvements, so this got me curious about why they did not offer any extended life and why bolts seem to break so early.
I did some searching but could not find anything pertaining to my question.
From what I have read the AR-15 bolt in an M4 under heavy firing schedules is generally good for 6-10,000 rounds, while bolts on piston guns seem to be good for 20,000 or so.
Im wondering what makes the difference? The bolt even in piston AR-15's seems to be made the exact same way as the standard bolt, but they seem to last longer.
Is this a material difference, the heat generated from the DI system or is it a little bit of both?
Where did you get your numbers? Especially those that relate to piston guns?
I will say this. In my experience unless someone starts with a virgin gun, there is no way to predict bolt life. Did they start with virgin guns when they did these tests?
Were the weapons properly lubed? What was the firing schedule?
The reason I ask is because I have at least one bolt right now that has over 7.5K rounds through it, many of those are suppressed and yet it seems to be fine. As a matter of fact I have only changed the ejector spring.
Exactly...
Shoot it until it breaks.
skullworks
06-04-12, 14:13
All things being equal, from a mechanical stand point, I fail to see how a bolt in a piston system will have a lower MTBF than a bolt in a DI system.
All things being equal, from a mechanical stand point, I fail to see how a bolt in a piston system will have a lower MTBF than a bolt in a DI system.
Heat transfer.
skullworks
06-04-12, 14:34
Heat transfer.
Well, I would agree with you if it wasn't for the fact that in a DI system the gas pressure pushes the bolt forward during unlock (minimizing friction between the bolt lugs and the lugs in the receiver extension); whereas in a piston system the bolt lugs have full engagement during unlock, thereby subjecting the bolt lugs to a higher level of stress throughout unlock compared to a DI system.
Therefore the question is what is more harmful: heat transfer or mechanical stress? In this case my money is on mechanical stress.
Well, no. Extraction occurs in exactly the same manner in an inline system and an op-rod system, as far as the amount of force on the bolt lugs are concerned.
I thought we covered that in this thread:
https://www.m4carbine.net/showthread.php?t=101258
sinlessorrow
06-04-12, 14:59
Well, no. Extraction occurs in exactly the same manner in an inline system and an op-rod system, as far as the amount of force on the bolt lugs are concerned.
I thought we covered that in this thread:
https://www.m4carbine.net/showthread.php?t=101258
Pretty much, to mch pressure at the chamber to press the bolt against it.
That said I was reading BB's posts on a different website and they were talking about maint. And one big thing was how on M4's bolts should be replaced every 4,000 but can go 10,000. Barrels should be replaced every 12,000.
They also mentioned how pistons greatly increase bolt life, thats what had me wondering, WHY do pistons greatly increase bolt life from 4,000-10,000 to 20,000?(on the HK and LWRCI guns)
Suwannee Tim
06-04-12, 15:02
Heat transfer.
I was pleasantly surprised to learn how little heat is transferred to the bolt, bolt carrier and upper behind the barrel. It was a lot less heat than I thought. I fired 300 rounds in about 20 minutes and none were more than warm. The barrel transfers a hell of a lot more heat to the upper than the DI system. There are claims that DI is easier on a bolt due to the forward thrust of the gasses which works against the rearward force on the bolt. I don't know if this is true or not. I would like to see some hard evidence or calculations.
Pretty much, to mch pressure at the chamber to press the bolt against it.
That said I was reading BB's posts on a different website and they were talking about maint. And one big thing was how on M4's bolts should be replaced every 4,000 but can go 10,000. Barrels should be replaced every 12,000.
They also mentioned how pistons greatly increase bolt life, thats what had me wondering, WHY do pistons greatly increase bolt life from 4,000-10,000 to 20,000?(on the HK and LWRCI guns)
KAC and LMT are making similar claims with their enhanced bolts, so I dont think its piston vs di as much as bolt construction.
I was pleasantly surprised to learn how little heat is transferred to the bolt, bolt carrier and upper behind the barrel. It was a lot less heat than I thought. I fired 300 rounds in about 20 minutes and none were more than warm. The barrel transfers a hell of a lot more heat to the upper than the DI system. There are claims that DI is easier on a bolt due to the forward thrust of the gasses which works against the rearward force on the bolt. I don't know if this is true or not. I would like to see some hard evidence or calculations.
I tried to find some slow-motion shots of the bolt cycling, to see if there was visible gas venting through the carrier and I couldn't find a shot that had any(so no video evidence to backup anything I have to say). Most of the broken bolts I've seen have been at the cam pin (I've never personally seen a broken lug) so I had always assumed that the heat transfer to the rear of the bolt is what would cause the failures.
I guess I've also never handled the bolt or carrier directly after a course of fire to feel how hot it was.
For a properly made and tested bolt, it should be fine for about 5,000 rounds even under heavy use. After that, it's going to have cracks and inclusions and COULD break at any time but that doesn't mean that it WILL break or that the expected life of a bolt is 5,000 rounds. There's plenty of old Colt rifles still being shot with their original bolts, but then on the other hand, there's plenty of new gun's being run harder than most AR's ever have which need replacement parts pretty often. Just own a well made bolt, shoot it wet, inspect it during your detailed cleaning sessions and replace it when it's questionable.
As far as piston bolts go, their bolts aren't AS exposed to the gas, heat, and pressure that a DI bolt is constantly subjected to, so that may be the difference, or it may just be another aspect of pistons that someone's hyping up and in reality, doesn't really matter.
KAC and LMT are making similar claims with their enhanced bolts, so I dont think its piston vs di as much as bolt construction.
I think you might be on to something.
skullworks
06-04-12, 16:00
I thought we covered that in this thread:
https://www.m4carbine.net/showthread.php?t=101258
You thought, but you were wrong (no disrespect intended). Please read the thread you linked again and you will (well, you should) see that you are incorrect. Yes, timing is important. But if timing is not adjusted (as in the "all things being equal" in my original statement) a piston system will subject the bolt lugs to a higher level of stress, whereby a DI system will be less abusive to the bolt than a piston system. Thus a DI system will incur longer bolt life than a piston system.
I read the BCG PiP for the M4 has been cancelled because none of the entrants offered any improvements, so this got me curious about why they did not offer any extended life and why bolts seem to break so early.
Perhaps it was more of an issue of the improved bolts not offering enough improvement to justify their extra cost? Some beancounters would argue that if your new widget costs twice as much as the old widget, it better have a service life twice as long, at minimum, to justify the change.
I haven't had a chance to read the original documents, but I also wouldn't be surprised if they wanted backward compatibility with the existing barrel extension. Some of the improved bolt designs require a proprietary barrel extension.
sinlessorrow
06-04-12, 16:11
You thought, but you were wrong (no disrespect intended). Please read the thread you linked again and you will (well, you should) see that you are incorrect. Yes, timing is important. But if timing is not adjusted (as in the "all things being equal" in my original statement) a piston system will subject the bolt lugs to a higher level of stress, whereby a DI system will be less abusive to the bolt than a piston system. Thus a DI system will incur longer bolt life than a piston system.
Thats great in theory but it seems the service life of a bolt is 5,000(before developing cracks) for the M4 while piston guns do indeed seem to last much longer.
I just cannot understand why. At first i thought heat but there is at max 40* difference, certainly not enough to induce such rapid wear. So maybe it does come down to construction, but what makes a bolt like the HK for example better constructed, the design of the bolt face and lugs appears to be identicle aside from finish.
To deawaters i know the BCG's entered had to be drop in, but even LWRCI claimed 20,000 ontheir DI bolt.
@Skullworks:
And why is that?
What is the difference between an op-rod pushing on the bolt carrier and the gas pushing on the bolt carrier when it comes to extraction? They both push the bolt carrier back, until the cam pin starts to move in the cam pin track, thus rotating the bolt until it unlocks.
There is no room inside the barrel extension for the gas to push the bolt forward. If there was, the gun would probably be unsafe to fire.
Both systems incur wear on the bolt lugs, as there will be a slight diagonal movement during unlock, where the bolt lugs on the bolt push against the bolt lugs in the extension. And case obturation has ceased by the time the bolt starts to extract the casing from the chamber.
Again, this is probably more related to bolt construction than DI vs piston. Also, like some of the guys with more expertise here said in previous posts, it is very hard to estimate bolt life. It will depend on how hard people run their guns, what kind of ammo they use, if the system is synced in terms of ammo, buffer weight and spring, what manufacturer made the bolt, etc.
Edit:
I just googled "Broken AR-15 bolts", and most of the pictures showed bolts that broke in two at the cam pin slot, and not sheared bolt lugs. Why they break in two in that specific area, I don't know.
We have never experienced that on our guns. The 10.5" guns have had some issues with broken disconnectors and sheard bolt lugs, during courses of fire shooting A LOT of ammo. If there is considerable carrier tilt in the 10.5" guns I don't know. I do know that the 16.5" guns are holding up well, and as a comparison, we see way more broken Aimpoints than guns.
skullworks
06-04-12, 16:30
Thats great in theory but it seems the service life of a bolt is 5,000(before developing cracks) for the M4 while piston guns do indeed seem to last much longer.
Seems? Do you have definitive numbers for both systems?
sinlessorrow
06-04-12, 16:33
Seems? Do you have definitive numbers for both systems?
No definitive number but everything ive read from SME's like BB says to replace the bolt at 4,000-5,000 cause thats when they develop crack but they may go to 7,000-10,000 if your lucky.
On the other hand the same people say piston AR's bolt have greatly increased service life and can go 15,000-20,000 before needing to be replaced
I am just wondering why. What makes the construction of bolts like the HK bolt so much better? The lugs and extractor appear to be the same dimension.
ETA to add: the 4-5k is under heavy firing schedules same for the piston numbers
skullworks
06-04-12, 16:46
There is no room inside the barrel extension for the gas to push the bolt forward. If there was, the gun would probably be unsafe to fire.
Please note that there is a difference between pushing the bolt forward so that is has NO contact with the BE lugs and pushing it forward so it has LESS pressure during contact with the BE lugs. What I am saying is that the DI system pushes the bolt forward so that it has LESS pressure on the lugs during contact than when rotated in a piston system. Therefore less stress is incurred on the bolt and BE lugs in a DI system than in a piston system, whereby the bolt life should be longer in a DI system (from a purely mechanical standpoint).
I think its a toss up, the di has less wear and stress, the piston has less heat transfer, I could maybe see the piston getting a couple k more rounds but not 4x the life.
I think comparing a hk piston to a colt di is apples and oranges.
The only real way to solve this eternal debate it to get 2 (or 20) identical rifles (lets say lmt mrp's) one piston, one di and shoot the shit out of them until failure.
sinlessorrow
06-04-12, 16:52
Please note that there is a difference between pushing the bolt forward so that is has NO contact with the RE lugs and pushing it forward so it has LESS contact with the RE lugs. What I am saying is that the DI system pushes the bolt forward so that it has LESS contact than when rotated in a piston system. Therefore less stress is incurred on the bolt and RE lugs in a DI system than in a piston system, whereby the bolt life should be longer in a DI system (from a purely mechanical standpoint).
This is what I always thought to, and why I am so confused on the 5,000(M4) vs 15,000(piston).
ETA: to viper, the reason I mentioned BB is because he sees alot of rifles and is where i got these number.
@Skullworks:
Not to nitpick, but you are saying bolt lugs in the receiver extension, but you are actually talking about the barrel extension. The reciever extension is where the buffer and action spring goes.
And how can there be less contact?
When the bolt is locked forward, the entire BCG is pushed forward by the action spring. As the cartridge is fed into the chamber, the bolt rotates as the cam pin rides along the cam pin track, and is locked by aligning the lugs on the bolt with the lugs in the barrel extension. The bolt is also pushed to the rear by the cartridge itself, as it stops at the neck of the chamber.
Now, as the the bolt carrier starts to move to the rear at the beginning ot the unlocking phase, how can there be less contact between the bolt lugs, when the case that is stuck to the chamber walls is keeping the bolt pushed back against the lugs in the barrel extension?
I'm not beating a piston drum here, I am simply stating that both designs, in terms of wear on the bolt lugs, are the same.
The only real way to solve this eternal debate it to get 2 (or 20) identical rifles (lets say lmt mrp's) one piston, one di and shoot the shit out of them until failure.
Sounds good. If you're buying then I'll take one of each and let you know how it goes. :)
@Skullworks:
Not to nitpick, but you are saying bolt lugs in the receiver extension, but you are actually talking about the barrel extension. The reciever extension is where the buffer and action spring goes.
And how can there be less contact?
When the bolt is locked forward, the entire BCG is pushed forward by the action spring. As the cartridge is fed into the chamber, the bolt rotates as the cam pin rides along the cam pin track, and is locked by aligning the lugs on the bolt with the lugs in the barrel extension. The bolt is also pushed to the rear by the cartridge itself, as it stops at the neck of the chamber.
Now, as the the bolt carrier starts to move to the rear at the beginning ot the unlocking phase, how can there be less contact between the bolt lugs, when the case that is stuck to the chamber walls is keeping the bolt pushed back against the lugs in the barrel extension?
I'm not beating a piston drum here, I am simply stating that both designs, in terms of wear on the bolt lugs, are the same.
You are and they are not. You are beating the piston drum in your own special way and the physics of unlocking between the two are not the same. If ever there were a case to argue apples and oranges, this is it.
Well, perhaps you would care to expound on the issue? Aside from the fact that one uses an op-rod, and one uses gas, what is the physical difference between the two systems in terms of unlocking and bolt lug wear rates?
And why did many of the pictures my google search turned up show AR-15 bolts broken at the cam pin slot?
I am posing a real question, not being argumentative.
And I assure you I am not beating a piston drum. I am only commenting as that is the system with which I have the most experience. If my views and experiences with that particular system is not welcome, fine, I'll stop commenting. We are however, the single largest user of a piston AR system, and have had some experience with it.
And if I have acted unprofessional or behaved improperly, point it out and I will adjust accordingly.
I find it odd however, that MistWolf says the same thing in the thread I linked to, but I am a piston drum beater.
Heavy Metal
06-04-12, 17:52
Heat transfer.
Why? The BCG gets nowhere near hot enough to affect the temper of the steel. A couple hundred degrees at best.
Hey guys I have a question on bolts. I read the BCG PiP for the M4 has been cancelled because none of the entrants offered any improvements, so this got me curious about why they did not offer any extended life and why bolts seem to break so early.
I did some searching but could not find anything pertaining to my question.
From what I have read the AR-15 bolt in an M4 under heavy firing schedules is generally good for 6-10,000 rounds, while bolts on piston guns seem to be good for 20,000 or so.
Im wondering what makes the difference? The bolt even in piston AR-15's seems to be made the exact same way as the standard bolt, but they seem to last longer.
Is this a material difference, the heat generated from the DI system or is it a little bit of both?
Bolt breakage causations aside, I'm surprised that the KAC E3 and LMT bolts didn't showed markedly better lifespan. Maybe the E3 didn't qualify due to the barrel extension differences?
Sent from my DROID RAZR using Tapatalk 2
sinlessorrow
06-04-12, 19:57
Bolt breakage causations aside, I'm surprised that the KAC E3 and LMT bolts didn't showed markedly better lifespan. Maybe the E3 didn't qualify due to the barrel extension differences?
Sent from my DROID RAZR using Tapatalk 2
Only Remington, S&W, and LWRCI submitted designs. The LWRCI is a nice BCG and i just cant believe it didnt offer an upgrade with its impressive extractor, to me either my friend is wrong or the Army is a bunch of idiots......probably the latter
Suwannee Tim
06-04-12, 20:10
......On the other hand the same people say piston AR's bolt have greatly increased service life and can go 15,000-20,000 before needing to be replaced......
Who says?
sinlessorrow
06-04-12, 20:23
Who says?
BB over on LF.
G3Kurz.
Ive seen it mentioned in a few threads here about the 416
And a few more
Bingo!
Why? The BCG gets nowhere near hot enough to affect the temper of the steel. A couple hundred degrees at best.
what is the physical difference between the two systems in terms of unlocking and bolt lug wear rates?
Op-rod shoves carrier back and bolt gets ripped out of barrel extension.
Conventional system has gas expanding in a chamber that pushes bolt forward and carrier rearward simultaniously, but as the bolt travel is blocked by everything in front of it, the carrier moves backward as a result.
The camming action is a function of the bolt cam pin moving in its guide, but in OR the carrier goes backward pulling the cam through its track while DI pushes bolt and carrier apart from the middle giving less stress on the cam pin and bolt in general.
With good balance in DI there will be no more stress applied to the cam pin during unlocking and actual travel action than you would induce by manipulating it by hand.
Reaching end of travel will obviously apply a force, but from when motion starts til end of travel, the pin is basically floating and mostly getting resistance from the carrier cam slot turning/guiding it off from a straight path of travel and whatever drag the firing pin passing through it applies.
This doesn't occur in OR due to the carrier doing 100% pulling on the bolt to move things.
Basically the difference between putting a jack between two objects to move them apart from each other through application of even force loads (DI) vs using a big slide hammer on the outside of one of the objects to yank it away from the other by brute force (OR)
And why did many of the pictures my google search turned up show AR-15 bolts broken at the cam pin slot?
Likely because they were the result of old or out of spec bolts, hot rounds, or overgassing.
The latter pair would cause the cam pin to be slammed into the forward end of the carrier cam slot with significantly more force than normal.
Net result is breakage at the narrowest/thinnest/weakest point, the sides of the bolt's cam pin hole.
If the hardened bolt is of top of expected spec quality by virtue of the stars, molecules, manufacture or whatever, it will be strong enough in that area to resist fracturing resulting in the alternate carrier group failure from hot round or over gassing: a guillotined cam pin.
Cam pins are not of the same material or hardness of a bolt or even a carrier making it the easiest to shear even though its diameter gives it greatly more surface area than the wee little sides of the bolt cam pin hole. Nor can it resist the outright mass of the carrier proper.
Thats great in theory but it seems the service life of a bolt is 5,000(before developing cracks) for the M4 while piston guns do indeed seem to last much longer.
Aren't you the one who owns a full auto lower? What has been your experience?
sinlessorrow
06-04-12, 23:13
Aren't you the one who owns a full auto lower? What has been your experience?
I wish, sadly all my rifles are Semi. I have used AUTO lowers but none are personally owned
Op-rod shoves carrier back and bolt gets ripped out of barrel extension.
Conventional system has gas expanding in a chamber that pushes bolt forward and carrier rearward simultaniously, but as the bolt travel is blocked by everything in front of it, the carrier moves backward as a result.
The camming action is a function of the bolt cam pin moving in its guide, but in OR the carrier goes backward pulling the cam through its track while DI pushes bolt and carrier apart from the middle giving less stress on the cam pin and bolt in general.
With good balance in DI there will be no more stress applied to the cam pin during unlocking and actual travel action than you would induce by manipulating it by hand.
Reaching end of travel will obviously apply a force, but from when motion starts til end of travel, the pin is basically floating and mostly getting resistance from the carrier cam slot turning/guiding it off from a straight path of travel and whatever drag the firing pin passing through it applies.
This doesn't occur in OR due to the carrier doing 100% pulling on the bolt to move things.
Basically the difference between putting a jack between two objects to move them apart from each other through application of even force loads (DI) vs using a big slide hammer on the outside of one of the objects to yank it away from the other by brute force (OR)
Likely because they were the result of old or out of spec bolts, hot rounds, or overgassing.
The latter pair would cause the cam pin to be slammed into the forward end of the carrier cam slot with significantly more force than normal.
Net result is breakage at the narrowest/thinnest/weakest point, the sides of the bolt's cam pin hole.
If the hardened bolt is of top of expected spec quality by virtue of the stars, molecules, manufacture or whatever, it will be strong enough in that area to resist fracturing resulting in the alternate carrier group failure from hot round or over gassing: a guillotined cam pin.
Cam pins are not of the same material or hardness of a bolt or even a carrier making it the easiest to shear even though its diameter gives it greatly more surface area than the wee little sides of the bolt cam pin hole. Nor can it resist the outright mass of the carrier proper.
Well said. Cam pin lash is much more violent in an op rod gun. This is evidenced by the rear corner of the cam pin clearance cut in the upper getting peened over. Colt addressed this issue in its op rod carbine by lengthening the clearance cut and installing a steel strike plate.
Well said. Cam pin lash is much more violent in an op rod gun.
Prove it.
I've seen virtually identical wear on my DI guns vs. piston guns. I generally normalizes out and has zero to do with long term function.
This is evidenced by the rear corner of the cam pin clearance cut in the upper getting peened over. Colt addressed this issue in its op rod carbine by lengthening the clearance cut and installing a steel strike plate.
Solution in search of a problem
If they really wanted to take care of it right instead of making it look like they're doing something by adding to the cost, they would machine the upper correctly to account for this.
constructor
06-05-12, 11:18
@Skullworks:
And why is that?
What is the difference between an op-rod pushing on the bolt carrier and the gas pushing on the bolt carrier when it comes to extraction? They both push the bolt carrier back, until the cam pin starts to move in the cam pin track, thus rotating the bolt until it unlocks.
There is no room inside the barrel extension for the gas to push the bolt forward. If there was, the gun would probably be unsafe to fire.
Both systems incur wear on the bolt lugs, as there will be a slight diagonal movement during unlock, where the bolt lugs on the bolt push against the bolt lugs in the extension. And case obturation has ceased by the time the bolt starts to extract the casing from the chamber.
Again, this is probably more related to bolt construction than DI vs piston. Also, like some of the guys with more expertise here said in previous posts, it is very hard to estimate bolt life. It will depend on how hard people run their guns, what kind of ammo they use, if the system is synced in terms of ammo, buffer weight and spring, what manufacturer made the bolt, etc.
Edit:
I just googled "Broken AR-15 bolts", and most of the pictures showed bolts that broke in two at the cam pin slot, and not sheared bolt lugs. Why they break in two in that specific area, I don't know.
We have never experienced that on our guns. The 10.5" guns have had some issues with broken disconnectors and sheard bolt lugs, during courses of fire shooting A LOT of ammo. If there is considerable carrier tilt in the 10.5" guns I don't know. I do know that the 16.5" guns are holding up well, and as a comparison, we see way more broken Aimpoints than guns.
The piston on the rear of the bolt causes as much forward pressure as rearward pressure since they push against each other. It doesn't move the bolt forward but some pressure is better than no pressure like on a piston rifle.
ETA- I have always seen more bolts break at the cam pin hole than the lugs as long as the receiver face is square and all lugs share an equal amount of the force.
sinlessorrow
06-05-12, 12:23
an update about the BCG PiP, I talked to my friend who was able to get some details about it but he couldnt tell me everything.
He said the BCG PiP had to be at least 25% better in all areas in order to get selected. Unfortunately none of the entry's reached that 25%. That is why the BCG PiP was cancelled, at most they were getting around 10-15% increase in performance and bolt life but most cost nearly double what the standard BCG cost.
its also good to see constructor chiming in.
constructor
06-05-12, 12:56
I would have liked to have made our bolts to the best design possible which IMO is like the knight E3 design of the lugs but I knew I had to make the lugs work with existing barrel extensions in order to sell bolts so I made them as large as I possibly could and still pass through the extension slots.
Making the cam pin slightly smaller is another option to strengthen the bolt but that would require making cam pins and again add another special part to the list.
Stronger alloys can increase strength but double the cost of the material. That isn't much but when the machines rate of cut are slowed down to cut the material the production cost can double easily.
skullworks
06-05-12, 12:58
@Skullworks:
Not to nitpick, but you are saying bolt lugs in the receiver extension, but you are actually talking about the barrel extension. The reciever extension is where the buffer and action spring goes.
You are correct; I meant barrel extension - I was still tired from Danish Open. ;)
As to the rest of my argument others have explained it in greater detail and in more eloquent ways since my last post.
sinlessorrow
06-05-12, 13:27
I would have liked to have made our bolts to the best design possible which IMO is like the knight E3 design of the lugs but I knew I had to make the lugs work with existing barrel extensions in order to sell bolts so I made them as large as I possibly could and still pass through the extension slots.
Making the cam pin slightly smaller is another option to strengthen the bolt but that would require making cam pins and again add another special part to the list.
Stronger alloys can increase strength but double the cost of the material. That isn't much but when the machines rate of cut are slowed down to cut the material the production cost can double easily.
that is exactly why the BCG PiP was dropped, they had to work with the existing barrel extension, and they had to be able to use the standard cam pins.
with those set parameters nothing offered even a 25% increase but all cost nearly double.
Constructor what is your experience with bolt life pertaining to the questions int he OP?
constructor
06-05-12, 13:43
that is exactly why the BCG PiP was dropped, they had to work with the existing barrel extension, and they had to be able to use the standard cam pins.
with those set parameters nothing offered even a 25% increase but all cost nearly double.
Constructor what is your experience with bolt life pertaining to the questions int he OP?
I don't know about those numbers, I've never seen test results from someone or some company I would believe. From what I have seen the piston rifle bolts don't last as long as DI bolts. I've had several manufacturers of piston rifles contact us about making bolts for them because of problems with bolt life.
Look for companies who have changed either the bolt design or cam pin or both as a clue to where the problems are.
I have never tried to run any tests with all of the different piston platforms out there and compare that to DI rifles to see how long bolts will run. It would take several firearms of each type to average out the life span and a crapload of ammo. Way too much expense for me.
sinlessorrow
06-05-12, 17:48
I don't know about those numbers, I've never seen test results from someone or some company I would believe. From what I have seen the piston rifle bolts don't last as long as DI bolts. I've had several manufacturers of piston rifles contact us about making bolts for them because of problems with bolt life.
Look for companies who have changed either the bolt design or cam pin or both as a clue to where the problems are.
I have never tried to run any tests with all of the different piston platforms out there and compare that to DI rifles to see how long bolts will run. It would take several firearms of each type to average out the life span and a crapload of ammo. Way too much expense for me.
thats interesting and certainly good information, I have to agree the man parts of breakage seem to be the cam pin area and the 2 lugs around the extractor.
I have read a few people say the heat is what kills the DI bolt earlier but there honestly is not that huge of a difference in heat, but im also not a metallurgist so idk how much heat it takes to really damage a bolt or make it more brittle.
constructor
06-05-12, 19:09
thats interesting and certainly good information, I have to agree the man parts of breakage seem to be the cam pin area and the 2 lugs around the extractor.
I have read a few people say the heat is what kills the DI bolt earlier but there honestly is not that huge of a difference in heat, but im also not a metallurgist so idk how much heat it takes to really damage a bolt or make it more brittle.
9310 alloy takes apx 1200 degrees to hurt the heat treat, it will drop it 1 point. TiAlN is applied at 940 degrees and does not hurt the hardness of the bolts. 900 degrees would probably cook off the ammo.
IMO heat only evaporates the lube on the carrier and bolt and slows down the cycling, that along with the soot can really slow things down.
The military performed a long test on bolts and concluded the broken lugs started from stress cracks and pits from corrosion. The breaks at the cam pin start from stress cracks also, some bolts are too hard and brittle from using the wrong heat treat or from the bolts being hardened too much. The guys that run the furnace make mistakes just like anyone else.
Bolts are cheap 1 -3 gun event will cost more money in ammo than the bolt cost. 5 years ago I broke a new chrome 556 bolt at the cam pin hole in 1 day of shooting,round count min was 400 for all of the stages.
Knowing I had a new bolt in there I did not take a spare...now I keep a complete BCG in my dump bag.
sinlessorrow
06-05-12, 20:22
9310 alloy takes apx 1200 degrees to hurt the heat treat, it will drop it 1 point. TiAlN is applied at 940 degrees and does not hurt the hardness of the bolts. 900 degrees would probably cook off the ammo.
IMO heat only evaporates the lube on the carrier and bolt and slows down the cycling, that along with the soot can really slow things down.
The military performed a long test on bolts and concluded the broken lugs started from stress cracks and pits from corrosion. The breaks at the cam pin start from stress cracks also, some bolts are too hard and brittle from using the wrong heat treat or from the bolts being hardened too much. The guys that run the furnace make mistakes just like anyone else.
Bolts are cheap 1 -3 gun event will cost more money in ammo than the bolt cost. 5 years ago I broke a new chrome 556 bolt at the cam pin hole in 1 day of shooting,round count min was 400 for all of the stages.
Knowing I had a new bolt in there I did not take a spare...now I keep a complete BCG in my dump bag.
great info, is there any public documents on the testing in red? would be interesting to read. what is considered corrosion
constructor
06-05-12, 21:09
great info, is there any public documents on the testing in red? would be interesting to read. what is considered corrosion
There is. It was on arfcom about 5 years ago. I'll look around to see if i can find it.
They were talking about pits on the bolt face, some due to gases leaking around the primer.
This will take more than 1 post--
Failure Analysis of the M16 Rifle Bolt
V.Y. Yu*, J.G. Kohl, R.A. Crapanzano, M.W. Davies, A.G. Elam, M.K. Veach
Department of Civil and Mechanical Engineering
United States Military Academy
West Point, NY 10996, USA
Phone: 011.845.938.5507 Fax: 011.845.938.5522
Email: Victor.Yu@usma.edu*
Abstract
Recently, there have been several occurrences of failure in the bolt of the M16 rifle at a United States Army installation. Near the failure location, the bolt was subjected to repeated loading as the M16 was fired. In order to determine the stress distribution of the bolt due to the firing process, a geometric element analysis was performed using ProMechanica®. The fracture surface was examined using both an optical stereomicroscope and a scanning electron microscope in order to determine failure initiation and failure mode. It was discovered that the fracture initiated at a localized corrosion pit and propagated by fatigue. A controlled experiment, consisting of firing 1800 rounds using new bolts, showed that a region of wear developed near the site where fracture occurred in the failed bolt. This suggests that exposure of the base metal may have facilitated the formation of corrosion pits. In addition, Vickers microhardness profiles were taken on cross-sectional areas near the fillet region and 10 mm away from the failed locking lug. Disparities between microhardness profiles near the fillet region and 10 mm away from this region revealed that the bolt may not have been uniformly case hardened.
Keywords: failure analysis, abrasive wear, corrosion, geometric element analysis
1. Introduction
The M16 rifle was fielded into the U.S. Army in 1968 during the Vietnam War. The rifle has since been the primary assault rifle used by U.S. soldiers. The M16 has been through several modifications in its more than 30 years of service in the military. In July of 2003, an increasing trend in the amount M16A2 bolt failures was observed at a U.S. Army installation. Figure 1 displays the data of bolt failures observed over a five year span. These rifles were used over the past nine years during summer military training. As a result, this paper investigates the leading cause of catastrophic fracture of the bolt under firing conditions.
This study used both a geometric element analysis and a metallurgical analysis of the bolt. The goals of the methodology used are that 1) the geometric element analysis would reveal whether any elevated stresses existed in the bolt which would facilitate crack initiation and propagation; and 2) the metallurgical analysis would determine the fracture origin and failure mechanism. The metallurgical analysis would also determine whether mechanical properties of the material were insufficient for the designed operation of the bolt.
A controlled experiment was conducted which consisted of firing 1800 rounds using new bolts. After 1800 rounds, it was observed that there existed wear patterns which exposed new base metal to the environment at the same location as the failure initiation site on the fractured bolt. This exposed base metal may therefore serve as a site for corrosion pitting.
2. Geometric Element Analysis
2a. Procedure. In order to analyze the stresses that the bolt experienced while firing, a three-dimensional model of the bolt generated in Pro-Engineer® was used [1]. Figure 2 displays the three-dimensional model of the bolt. Subsequently, Pro-Mechanica® was used to post-process the model in order to calculate the von-Mises stresses in the bolt. Pro-Mechanica® differs from traditional finite element packages in that it does not use linear shape functions. Instead, Pro-Mechanica® fits polynomials up to 9th order as the shape function and is termed geometric element analysis. Thus, geometric element analysis offers accurate computational results even if the mesh is coarse, since the polynomials offer better convergence to the shape functions. As a result, the generated model of the bolt does not use purely linear shape functions since it can incorporate complex polynomials to fit the shape function. Furthermore, since a coarser mesh can be used to generate an accurate approximation of the model, bi-linear quadrilaterals were not solely used; instead, a mix of triangular elements and bi-linear quadrilaterals were incorporated into the model as shown in Figures 3a and 3b.
From historical data at the U.S. Army’s Testing and Armament Command (TACOM) and the Army Research Laboratory, a stress of 414 MPa was used to model the instantaneous force of the propellant combustion of the 5.56 mm round in the M16 rifle on the face of the M16 bolt. The conventional method for converting this type of dynamic process to a static analysis assumes that during the actual firing of the weapon, the pressure in the cartridge after combustion is dissipated by the rearward motion of the bolt. In order to conduct a static analysis of the bolt, half of the cartridge pressure was used to model this dissipation of energy [2]. Therefore, a stress of 207 MPa was used as a distributed load on the face of the bolt in the model. This force modeled the impact of the propellant igniting and exploding within the combustion chamber without incorporating the effects of recoil and the buffer assembly in the rifle. In addition, boundary constraints were placed on the bolt which allowed for minute deformations that the bolt would experience when the cartridge exploded in the combustion chamber.
2b. Results and Discussion. The von-Mises stress distribution in the bolt showed high stress concentrations present at the fillet of the locking lugs as shown in Figures 4a and 4b. In particular, higher stress concentrations were present in the locking lugs which were immediately adjacent to the round extractor. These two specific locking lugs experienced stresses on the magnitude of approximately 1070 MPa as shown in Figure 4b. All of the five fractured bolts analyzed at the Army installation had fractured at these specific locking lugs. Figure 5a shows a picture of a fractured bolt specimen and Figure 5b shows a picture of the fractured specimen at higher magnification. In addition, these extremely high stress concentrations contributed to the crack initiation which is evidenced by the picture of a crack growing from the locking lug next to the round extractor, as shown in Figure 6.
3. Metallurgical Analysis
3a. Procedure. The M16 bolt was also analyzed from a metallurgical viewpoint. This analysis determined whether additional factors other than stress concentrations contributed to the bolt failure. A chemical analysis of the bolt was conducted to determine if the material specifications were met, as displayed in Table 1. A stereomicroscope and a SEM were used to locate the fracture origin and to evaluate the fracture surface.
Vickers microhardness indentation was performed on a cross-sectional area near the fillet of the lug and at approximately 10 mm away from the lug on the bolt. Indentation profiles, consisting of five indents for each location, were taken which started 0.5 mm from the surface of the bolt and proceeded inward every 0.5 mm. Hardness readings are shown in Table 2.
In addition, a controlled experiment was conducted where three new bolts were subjected to the firing of a total of 1800 rounds. The experiment entailed firing the bolts in 300 round increments and subsequently cleaned with Royco 634 cleaner, lubricant, and preservative (MIL-PRF-63460D AM6) after each iteration. After the 1800 rounds were fired, the surface of each bolt was then examined using a stereomicroscope to detect any surface anomalies which might have occurred.
3b. Results and Discussion. Chemical analysis of the bolt composition revealed no significant differences between the failed bolt and Carpenter Steel 158 specifications [3], as shown in Table 1. Micrographs from a SEM revealed that the M16 bolt experienced corrosion in the form of localized pitting, as shown in Figure 7, near the locking lugs adjacent to the round extractor. From the SEM micrographs, the circumference of the fracture surface of the ruptured locking lug possessed shear lips. The existence of the shear lips signified ductile failure at the surface. However, the region at the corrosion pit did not have this characteristic shear lip. The absence of the shear lip at this location indicates that the bolt material was discontinuous at the surface. This discontinuity suggests that the corrosion pit is where failure initiated. The corrosion pit provides an additional stress concentration which aids in the initiation of the crack. In addition, the SEM micrograph displayed the presence of chevrons as seen in Figure 7. The chevron markings point back to the localized pit which further confirmed that the pit was the site for crack initiation.
Near the initiation site, the fracture surface was transgranular with faint fatigue striations indicating fatigue crack growth, as shown in Figure 7 and 8. Approximately 2.5 mm from the crack initiation site, the fracture surface transitioned from a smooth surface to a dimpled surface. This dimpled surface signified that the crack experienced unstable crack growth, or ductile failure, in this region.
constructor
06-05-12, 21:15
continued-
The Vickers microhardness indentations taken at both locations show that the hardness reading is higher at the surface than towards the center of the bolt. This demonstrates that the surface was case hardened. However, the Vickers microhardness at the surface near the lug’s fillet was 100 units less than the hardness readings 10 mm from the fillet region. This indicates that the bolt was not uniformly case hardened. Thus, the softer region near the locking lugs is more susceptible to wear.
After 1800 rounds were fired using the new bolts, wear was observed which exposed the Carpenter steel 158 base metal to the environment, as shown in Figure 9. This area of observed wear on the surface of the bolt was in the same location as the crack initiation site on the fractured bolt, namely in the fillet region of the locking lugs adjacent to the round extractor. The base metal exposed due to the wear makes this specific area highly susceptible to corrosion pitting.
4. Conclusions
The fracture of the M16 bolt resulted from a cumulative effect of high stress concentrations at the fillet radius and the additional stress concentration imposed by the presence of localized pitting at the surface. The bolt possesses many fillet regions which impose numerous areas of high stress concentration. In particular, two fillets experienced higher stress immediately adjacent to the round extractor due to the non-contiguous feature of the bolt. These two specific areas of high stress concentration also corresponded to the same location where failure of the bolt occurred in all fractured bolt specimens. Micrographs obtained from the scanning electron microscope of the fractured surface showed localized pitting at the failure initiation site. In addition, transgranular crack propagation near the pit formations in the fillet regions was observed. The localized pits formed near the locking lugs also served as high stress concentration points. The presence of pits in the material amplified the stresses of the bolt in the locking lug region which already had a high stress concentration due to the irregular geometry of the bolt. This cumulative stress concentration provides a good indicator why the crack initiated and propagated from this region.
The wear observed in the controlled experiment indicates the mechanism of why the corrosion pits formed near the locking lug fillet by exposing the Carpenter Steel 158 base metal to the environment. Vickers microhardness readings near the fillet region show that the bolt was not uniformly case hardened. Comparison of the microhardness readings near the fillet region and 10 mm from this region show a disparity of approximately 100 units. The softer, less carburized region near the fillet contributes to the formation of a wear area after firing just 1800 rounds.
5. Acknowledgements
The authors would like to thank Mr. Victor K. Champagne, Jr. and the Materials Analysis Group at the Army Research Laboratory in Aberdeen Proving Grounds, MD for helpful discussions and for performing SEM work.
6. References
[1] Three-dimensional Pro-Engineer® model of M16 bolt from U.S. Army Testing and Armament Command, Rock Island, IL.
[2] Individual Weapon Systems & 3-D Technical Data Development Team, U.S. Army Testing and Armament Command, Rock Island, IL
That is the "weakest"part of the bolt. I like the AR but the problem is was designed by an aircraft person . That is why the absolute quality of the parts is necessary.The AK was built by a tank driver!!! Aircraft vs tractor.
sinlessorrow
06-05-12, 22:52
continued-
The Vickers microhardness indentations taken at both locations show that the hardness reading is higher at the surface than towards the center of the bolt. This demonstrates that the surface was case hardened. However, the Vickers microhardness at the surface near the lug’s fillet was 100 units less than the hardness readings 10 mm from the fillet region. This indicates that the bolt was not uniformly case hardened. Thus, the softer region near the locking lugs is more susceptible to wear.
After 1800 rounds were fired using the new bolts, wear was observed which exposed the Carpenter steel 158 base metal to the environment, as shown in Figure 9. This area of observed wear on the surface of the bolt was in the same location as the crack initiation site on the fractured bolt, namely in the fillet region of the locking lugs adjacent to the round extractor. The base metal exposed due to the wear makes this specific area highly susceptible to corrosion pitting.
4. Conclusions
The fracture of the M16 bolt resulted from a cumulative effect of high stress concentrations at the fillet radius and the additional stress concentration imposed by the presence of localized pitting at the surface. The bolt possesses many fillet regions which impose numerous areas of high stress concentration. In particular, two fillets experienced higher stress immediately adjacent to the round extractor due to the non-contiguous feature of the bolt. These two specific areas of high stress concentration also corresponded to the same location where failure of the bolt occurred in all fractured bolt specimens. Micrographs obtained from the scanning electron microscope of the fractured surface showed localized pitting at the failure initiation site. In addition, transgranular crack propagation near the pit formations in the fillet regions was observed. The localized pits formed near the locking lugs also served as high stress concentration points. The presence of pits in the material amplified the stresses of the bolt in the locking lug region which already had a high stress concentration due to the irregular geometry of the bolt. This cumulative stress concentration provides a good indicator why the crack initiated and propagated from this region.
The wear observed in the controlled experiment indicates the mechanism of why the corrosion pits formed near the locking lug fillet by exposing the Carpenter Steel 158 base metal to the environment. Vickers microhardness readings near the fillet region show that the bolt was not uniformly case hardened. Comparison of the microhardness readings near the fillet region and 10 mm from this region show a disparity of approximately 100 units. The softer, less carburized region near the fillet contributes to the formation of a wear area after firing just 1800 rounds.
5. Acknowledgements
The authors would like to thank Mr. Victor K. Champagne, Jr. and the Materials Analysis Group at the Army Research Laboratory in Aberdeen Proving Grounds, MD for helpful discussions and for performing SEM work.
6. References
[1] Three-dimensional Pro-Engineer® model of M16 bolt from U.S. Army Testing and Armament Command, Rock Island, IL.
[2] Individual Weapon Systems & 3-D Technical Data Development Team, U.S. Army Testing and Armament Command, Rock Island, IL
thanks for that, so are all bolts case hardened like that? is it possible to have a bolt evenly case hardened?
aslo from what I have read, and remember this is only information I have read from others on the internet(though supposedly SME's) what would make the HK416 bolt stronger than the M4 bolt?
That is the "weakest"part of the bolt. I like the AR but the problem is was designed by an aircraft person . That is why the absolute quality of the parts is necessary.The AK was built by a tank driver!!! Aircraft vs tractor.
im not sure what to think about this?
constructor
06-06-12, 00:29
thanks for that, so are all bolts case hardened like that? is it possible to have a bolt evenly case hardened?
I think some newer processes provide more uniform results but you know how the military is if it worked in 69 it should still work now. Mil spec bolts have a very strict heat treat procedure.
aslo from what I have read, and remember this is only information I have read from others on the internet(though supposedly SME's) what would make the HK416 bolt stronger than the M4 bolt?
?
Don't know about the 416 bolt, if they have figured out a way I am sure they protect that info. There are several alloys that are stronger than Carpenter 158.
The 416 bolt has a larger diameter overall then any DI bolt.
A DI bolt will fit into the 416 carrier with brand new gas rings on and it will move freely with no compression of the rings.
This increases the material thickness over the entire bolt, but more importantly, the areas to the sides of the cam pin hole are much thicker and stronger because of this.
The bolt lugs also *appear* to be slightly thicker as well. I will mic these in a little bit and compare.
The propretary allow HK uses probably also has something to do with it. It's obviously a high alloy steel with a fair amount of nickle in it based on the color, as well as some chrome. They almost look like they're machined NiB, if that makes sense.
They're made from the same alloy that the G36 bolts are made from, and i've had one (SL8 bolt actually) of those just sitting around, being unused, un-preserved, for the last 10 years, with 5 years of that in an unheated storage unit, and it's just now starting to show a few rust spots. Took the damn thing long enough.
I'll get back with the micrometer measurements on 416 bolt vs. USGI bolt in a bit.
I would add, that HK bolt gets also less thermal fatigue (heating to high temp and then cooling) than DI bolt - if used as directed (eg. as assault rifle or automatic rifle, not MG). In HK's that are abused by FA fire, when used in role of suppressive weapon (constant 'break contact' drills - dump mag(s), move, dump, move, da capo al fine), there are reports of bolt failure after about 10-15K rounds of such use.
Anyway, this shows that when increased thermal fatigue comes in place, there is no easy "workaround". Piston gun bolt usually gets less thermal fatigue, but even then, users are able to "kill them" by enough abuse.
It would be interesting to know what practical rpm ratio was used for cited research. There is mention 1800 rounds with cleaning every 300 rounds, but it is quite different thermal load when shooting one mag at 10rpm, then taking a break for 5 mins for next mag or shooting 10 mags in a row, even with same 10rpm pace (not to mention 20 or 30 rpm).
That is the "weakest"part of the bolt. I like the AR but the problem is was designed by an aircraft person . That is why the absolute quality of the parts is necessary.The AK was built by a tank driver!!! Aircraft vs tractor.
im not sure what to think about this?
If you're thinking that it's the kind of Elmer Fudd tripe that has no place in a technical discussion, you're on the right track.
SS, post because you have something to say, not because you simply feel like saying something.
My takeaway from all this is that the things that are important are: (1) proper heat treat, (2) proper materials and (3) proper machining/dimensional control.
Max pressure and force against the bolt is experienced when the bullet is only ~ 1" down the bore. That's when 55-60K pressures occur, well before the bullet gets close to the gas port. That's when the lugs are locked up tightest and the greatest stress is placed on the lugs. Everything after that, the pressure decreases. By the time the bullet has passed the port pressures are way down from max pressure shortly after firing.
If unlocking and extraction subjects the lug to forces, I have no idea. I could theoretically see some impacts to extractor wear if extraction is attempted while the case is still tightly gripping the walls, but as long as the case is in the "shrink back" phase after firing, I can't imagine any obvious wear issues. But again, I'm picturing this is an extractor issue, not a bolt issue.
Can anyone help clarify if I've got it right or wrong?
My takeaway from all this is that the things that are important are: (1) proper heat treat, (2) proper materials and (3) proper machining/dimensional control.
Max pressure and force against the bolt is experienced when the bullet is only ~ 1" down the bore. That's when 55-60K pressures occur, well before the bullet gets close to the gas port. That's when the lugs are locked up tightest and the greatest stress is placed on the lugs. Everything after that, the pressure decreases. By the time the bullet has passed the port pressures are way down from max pressure shortly after firing.
If unlocking and extraction subjects the lug to forces, I have no idea. I could theoretically see some impacts to extractor wear if extraction is attempted while the case is still tightly gripping the walls, but as long as the case is in the "shrink back" phase after firing, I can't imagine any obvious wear issues. But again, I'm picturing this is an extractor issue, not a bolt issue.
Can anyone help clarify if I've got it right or wrong?
I think that you have it right.
I would add, that HK bolt gets also less thermal fatigue (heating to high temp and then cooling) than DI bolt - if used as directed (eg. as assault rifle or automatic rifle, not MG). In HK's that are abused by FA fire, when used in role of suppressive weapon (constant 'break contact' drills - dump mag(s), move, dump, move, da capo al fine), there are reports of bolt failure after about 10-15K rounds of such use.
Anyway, this shows that when increased thermal fatigue comes in place, there is no easy "workaround". Piston gun bolt usually gets less thermal fatigue, but even then, users are able to "kill them" by enough abuse.
It would be interesting to know what practical rpm ratio was used for cited research. There is mention 1800 rounds with cleaning every 300 rounds, but it is quite different thermal load when shooting one mag at 10rpm, then taking a break for 5 mins for next mag or shooting 10 mags in a row, even with same 10rpm pace (not to mention 20 or 30 rpm).
Less thermal fatigue? What is considered high temperature? Exactly how hot does an HK 416 bolt get compared to an M4 bolt given the same firing cycle? Your statement can only lead me me to believe that you have vetted data to back up your facts.
The West Point engineering study is probably the most detailed military study on bolt wear conducted to date.
At the USAMU the average M16 rifleman will shoot around 2500-3500 rounds per barrel before primo championship-winning accuracy (defined as 10 and X-counts) starts to fall off and the Soldier requests a new barrel. The Custom Gun Shop replaces bolts after the third re-barreling, averaging around 9,000-10,000 logged rounds per new GI bolt.
I've broken a single Colt M4 bolt at the cam pin hole -- the weapon was a GI Colt M16A2 Carbine (723) in a close-quarters combat school student pool weapon. We did not know the round count on the gun but guessed it had been in service quite a while judging by the gas/flame cutting on the A2 flash suppressor slots.
A common problem with commercial chrome-plated AR components cracking is due to hydrogen embrittlement from improper plating.
Armalite has an interesting feature on their bolts in that the locking lug directly opposite the extractor groove is relieved differently to compensate for operation stress:
(quote -- Armalite has applied what it did on AR-10 bolts to their .233/5.56 bolts as well):
May 7, 1996
TECHNICAL NOTE 13: IMPROVED RIFLE BOLT
SUMMARY: The ArmaLite AR-10 rifle bolt bears an unusual improvement which may be mistaken for a defect: the locking lug opposite the extractor is deliberately relieved at the rear so as not to contact the locking lug of the barrel extension. This feature strengthens the bolt.
FACTS
1. ArmaLite bolts bear 7 locking lugs, each 22.5 degrees apart from the next. At this angle there should be 8 lugs in a circle, but one lug has been removed to provide space for the extractor.
2. The missing lug creates an asymmetry, or imbalance, in the bolt. When the rifle is fired the pressure of the cartridge presses the bolt rearward, and the lugs transfer this energy to the matching locking lugs of the barrel extension. The bolt flexes at the rear inside corner of the lug during this process. Because one lug is missing, the deformation is greatest in the area of the missing bolt. A series of engineering analyses have disclosed that the lugs on either side of the extractor each receive 40% of the recoil load.
3. Relieving the rear of the lug opposite the extractor "balances" the loading of the bolt by restoring symmetry. The load placed on the bolt is spread more evenly over the six remaining lugs. Peak lug loading is reduced.
4. Relieving the lug opposite the extractor reduces peak loading on the lugs neighboring the extractor from 40% to 24% each. It is not reduced to 16 1/3% (1/6 of the recoil load) because a small asymmetry remains: the lugs neighboring the extractor are slightly undercut for the extractor, which results in continued relative weakness at those lugs. Nonetheless, the load on the weakest lugs is reduced 40%, compared to the standard M-16 design, by spreading a portion of that load to the other 4 lugs.
5. In addition to the relieved lug, the AR-10 bolt bears tapered lugs with wide roots. This puts added strength exactly where stresses are at their greatest. The AR-10 bolt is significantly stronger than the similar M-16 bolt. A patent covering both bolt and barrel extension relief is pending.
MAW
Copyright © 1998 ArmaLite, Inc.
Less thermal fatigue? What is considered high temperature? Exactly how hot does an HK 416 bolt get compared to an M4 bolt given the same firing cycle? Your statement can only lead me me to believe that you have vetted data to back up your facts.
With same firing regime HK416 bolt is heated to lower temperatures than M4 bolt (you can check this by "touchy feely" after dumping mag trough both if more sofisticated equipment is not avaliable).
That means less heat transferred in one "heat-cool" cycle. Heat is representation of thermal (internal) energy (on molecular level) - more thermal energy means more changes to material internal structure (this is how heat hardening and tempering works). Actually temperature of parts is not so bad (if it is below last tempering temperature - otherwise hardening can be lost very fast). What is bad are constant cycles of heating and cooling. HK416 bolt gets less heat that M4 bolt (there is no heat from direct gases vented inside carrier also HK416 in some barrel length has significantly heavier barrel that works as bigger heat sink) and works in lower temperature (bolt itself is also heavier), so those heating-cooling cycles are less harmful. This is true to automotive engine parts (especially turbochargers) and is true to firearms parts. This or either I was told wrong, commie version of physics.
Please excuse me, English is not my mother-tongue and I sometime struggle a little trying to put concepts into words.
Armalite has an interesting feature on their bolts in that the locking lug directly opposite the extractor groove is relieved differently to compensate for operation stress:
Very interesting. I never tough of that, but there is strong logic. Physics love symmetry.
BB over on LF.
G3Kurz.
Ive seen it mentioned in a few threads here about the 416
And a few more
There is a .Mil 416 user on here that has told me many times that they typically break bolts on the 416 around 12k.
C4
that is exactly why the BCG PiP was dropped, they had to work with the existing barrel extension, and they had to be able to use the standard cam pins.
with those set parameters nothing offered even a 25% increase but all cost nearly double.
As we all know, Army is going through their down selection process for an M4 replacement. My thought is that once they have a winner, they will then test it head to head with the M4 and they will find out that it is NOT 25% better and cost is DOUBLE and drop the piston gun and stick with the M4.
Time will tell though.....
C4
I do not have M4 bolt at hand, but HK bolt is 0.528" (on my crappy caliper) diameter at cam pin hole.
sinlessorrow
06-06-12, 12:12
I would add, that HK bolt gets also less thermal fatigue (heating to high temp and then cooling) than DI bolt - if used as directed (eg. as assault rifle or automatic rifle, not MG). In HK's that are abused by FA fire, when used in role of suppressive weapon (constant 'break contact' drills - dump mag(s), move, dump, move, da capo al fine), there are reports of bolt failure after about 10-15K rounds of such use.
Anyway, this shows that when increased thermal fatigue comes in place, there is no easy "workaround". Piston gun bolt usually gets less thermal fatigue, but even then, users are able to "kill them" by enough abuse.
It would be interesting to know what practical rpm ratio was used for cited research. There is mention 1800 rounds with cleaning every 300 rounds, but it is quite different thermal load when shooting one mag at 10rpm, then taking a break for 5 mins for next mag or shooting 10 mags in a row, even with same 10rpm pace (not to mention 20 or 30 rpm).
Someone did a heat comparison on this website and bolt had a difference of 40* certainly not enough to cause damage according to Constructor which seems to require around 900*.
As we all know, Army is going through their down selection process for an M4 replacement. My thought is that once they have a winner, they will then test it head to head with the M4 and they will find out that it is NOT 25% better and cost is DOUBLE and drop the piston gun and stick with the M4.
Time will tell though.....
C4
Thats kind of how I feel about it too, Kevin B mentioned something similar and thats why they chose to focus on the PiP and opted out of the IC
There is a .Mil 416 user on here that has told me many times that they typically break bolts on the 416 around 12k.
C4
Excellen info, thanks for adding that.
To Sinister great post thats interesting about the barrel change every 3,000. Also adds a number to the bolt discussion beyond what I had.
I can certainly see an increase in material adding to strength. Will be interested to see the number diff between the two bolts
constructor
06-06-12, 12:24
I do not have M4 bolt at hand, but HK bolt is 0.528" (on my crappy caliper) diameter at cam pin hole.
That is our max size at the cam pin area also but because the carriers aren't always perfect(try to keep a bolt tail hole in the center when using a 5" long drill bit) we try to keep them at .526 for a little wiggle room.
sinlessorrow
06-06-12, 15:17
I do not have M4 bolt at hand, but HK bolt is 0.528" (on my crappy caliper) diameter at cam pin hole.
Ill measure m bolt tonight with mt calipers
Finally fount the micrometer.
M4 bolt = .512 OD at the cam pin
and .101 wall thickness at cam pin
HK bolt = .53 OD at the cam pin
and 1.11 wall thickness at cam pin.
M4 bolt = .101 lug thickness
HK bolt = .101 lug thickness.
Obviously, my eyes decieved me regarding lug thickness, but I was correct about the bolt diameter difference.
Like I said earlier, an M4 bolt fits freely into the MR556 carrier even with gas rings, but the HK bolt will only fit part way into an M4 carrier. It stops just before the cam pin hole is fully inside the carrier. This is caused by the piston ring bore on the inside of the carrier itself.
An examination of the HK bolt and the M4 bolt (noveske) show that the bolt lug joints (angles at the rear of the lugs where they transition from the rear of the lug into the rest of the bolt, a 90 degree transition)) are more radiused on the HK bolt, allowing for better fatigue resistance. Matter of fact, every angle and joint on the HK bolt is radiused, and to a better extent then anything on the DI bolt. Any metal worker will tell you that sharp angles create weak points in your material, and HK seems to have made every attempt to minimise this issue.
Not to beat the nitriding drum, but here are some thoughts regarding a real easy way to PiP the M4 system:
At this time, I have a single HK bolt that has been QPQ nitrided. I had my MR fully QPQ nitrided when I understood that this process imparted better corrosion resistance the chrome, had a lower coefficient of friction then chrome, and penetrated twice as deep as chrome plate adds to the steel. All great things.
What I learned AFTERWARDS, is that nitriding also increases the fatigue strength of the base material by nearly three times as much. Around 270%. Meaning that with the lower coeficient of friction (especially with lube added) between both a QPQ nitrided barrel/barrel extension and bolt, coupled with the increased fatigue strength of the nitriding process, my nitrided bolt should last an easy 20k rounds or more.
Looks like I need to send my spare off for nitriding as well, and I think that I'm going to start having all of my DI parts nitrided too.
At this point, I can't find a single negative aspect of nitriding gun parts.
Best part is that even a single dip nitride will enhance the base material greatly and it's a cheap process and when done in bulk, doesn't add a whole hell of a lot to the overall cost of a rifle.
If this became part of the TDP for Mil guns, I think they would find the overall performance of the M4/M16 platform increase greatly, with very little cost increase.
Heat transfer.
Why? The BCG gets nowhere near hot enough to affect the temper of the steel. A couple hundred degrees at best.
Yeah, I thought the heat transfer concern was thoroughly debunked with the use of thermal cameras and other technology...
It sounds like there are many variables when talking about bolt life:
manufacturer
type of steel used
QC of manufacturer
type of gas system (carbine/middy/rifle)
full auto fire
suppressed fire
lack of lubrication
Can there really be a definitive answer to the bolt life question?
Not to beat the nitriding drum, but here are some thoughts regarding a real easy way to PiP the M4 system:
At this time, I have a single HK bolt that has been QPQ nitrided. I had my MR fully QPQ nitrided when I understood that this process imparted better corrosion resistance the chrome, had a lower coefficient of friction then chrome, and penetrated twice as deep as chrome plate adds to the steel. All great things.
What I learned AFTERWARDS, is that nitriding also increases the fatigue strength of the base material by nearly three times as much. Around 270%. Meaning that with the lower coeficient of friction (especially with lube added) between both a QPQ nitrided barrel/barrel extension and bolt, coupled with the increased fatigue strength of the nitriding process, my nitrided bolt should last an easy 20k rounds or more.
Looks like I need to send my spare off for nitriding as well, and I think that I'm going to start having all of my DI parts nitrided too.
At this point, I can't find a single negative aspect of nitriding gun parts.
Best part is that even a single dip nitride will enhance the base material greatly and it's a cheap process and when done in bulk, doesn't add a whole hell of a lot to the overall cost of a rifle.
If this became part of the TDP for Mil guns, I think they would find the overall performance of the M4/M16 platform increase greatly, with very little cost increase.
Simplicity is always key IMHO.
Ive been very interested in QPQ since reading the nitriding thread. It seems to be a big improvement to metallurgy and firearms overall. Thinking about it now, from this post, if the numbers check out (added cost vs. added performance), it could be a viable direction, not to mention an easier transition for the military.
sinlessorrow
06-06-12, 20:33
Simplicity is always key IMHO.
Ive been very interested in QPQ since reading the nitriding thread. It seems to be a big improvement to metallurgy and firearms overall. Thinking about it now, from this post, if the numbers check out (added cost vs. added performance), it could be a viable direction, not to mention an easier transition for the military.
the issue is no one seemed to enter a Nitrided BCG, they were either phosphated or NiB which I have never been impressed with
What I would like to see is for Colt to be able to embrace some of the new(er) developments and products on the market to help improve the M4.
As we all know, Army is going through their down selection process for an M4 replacement. My thought is that once they have a winner, they will then test it head to head with the M4 and they will find out that it is NOT 25% better and cost is DOUBLE and drop the piston gun and stick with the M4.
Time will tell though.....
C4
Bill Alexander
06-06-12, 21:22
One must examine the interaction of specifically the nitrogen with chromium in higher alloys. While it is a generally sound statement that carbo nitriding QPQ will induce a surface compressional stress and as such increase tensile fatigue in many alloys, increased chromium may lead to a step function drop in the impact toughness. This has been seen to the extent that certain military prints will specifically preclude CN hardening on stressed components. Bolt alloys while not typically through hardening grades are very close in chemistry, carbo nitriding QPQ is best applied to case hardening alloys and low alloy steels with substantial bulk of design.
QPQ is not a new process and has its foundation in cyanide hardening. Melonite became the trade name of the salt bath carbo nitriding which was developed to remove the cyanide base. QPQ extended this process but to be truely effective the polishing phase must refine the surface. Regardless the process remains the diffusion of carbon and nitrogen free radicals into the surface of a steel alloy. The diffusion rate initially creates a sharp boundry between the substate and the underlying material which the quenching then develops by softening the transistion and conversion the alloy phase.
Bolts exist as high stress, low cycle fatigue components, in that the life is expressed in terms of less than 10^6 cycles under the operating load. What complicates the analysis is that during extraction the lugs are subject to biaxial stress, being both axial shear with tensile moment at the rear but also bending. Typically residual pressures during extraction can be as high as 3000 psi which will both impose load on the lugs but also hold the case to the chamber walls. Where this is leading is that given the load state of a bolt, the life is governed by crack initiation not propagation. Suface treatments that may assist the formation of micro cracks by lowering the impact strength, or alloys with such intergranular inclusions either as the result of treatment or residual tramp elements are best avoided. Hydrogen will dramatically shorten the bolt lfe as will any surface etching effects.
Ok, so in English, will QPQ reduce the impact toughness of a bolt and lead to a shorter round count life or not?
Alloys that create nitrides are typically contain aluminum, chromium, molybdenum and titanium. With this in mind, nitriding works better on metals that contain these metals, but not in excessive amounts as these metals can create very hard and very brittle (especially in the case of aluminum) nitrides that break easily and cause cracks to form. So the real question is at which amounts *will* these nitride creating metals create a situation where the surface loses its impact toughness? There were a lot of "mays" and "mights" in the above post, i'm looking for verifiable data please.
Same question for barrels and barrel extensions.
Also, does not the addition of the nitriding process lower the coefficient of friction between the materials, thusly reducing the stresses between parts? And since hydrogen isn't part of the nitriding process, nor is surface etching, how does your final statment factor into the equation?
BufordTJustice
06-07-12, 06:23
Finally fount the micrometer.
M4 bolt = .512 OD at the cam pin
and .101 wall thickness at cam pin
HK bolt = .53 OD at the cam pin
and 1.11 wall thickness at cam pin.
M4 bolt = .101 lug thickness
HK bolt = .101 lug thickness.
Obviously, my eyes decieved me regarding lug thickness, but I was correct about the bolt diameter difference.
Like I said earlier, an M4 bolt fits freely into the MR556 carrier even with gas rings, but the HK bolt will only fit part way into an M4 carrier. It stops just before the cam pin hole is fully inside the carrier. This is caused by the piston ring bore on the inside of the carrier itself.
An examination of the HK bolt and the M4 bolt (noveske) show that the bolt lug joints (angles at the rear of the lugs where they transition from the rear of the lug into the rest of the bolt, a 90 degree transition)) are more radiused on the HK bolt, allowing for better fatigue resistance. Matter of fact, every angle and joint on the HK bolt is radiused, and to a better extent then anything on the DI bolt. Any metal worker will tell you that sharp angles create weak points in your material, and HK seems to have made every attempt to minimise this issue.
Not to beat the nitriding drum, but here are some thoughts regarding a real easy way to PiP the M4 system:
At this time, I have a single HK bolt that has been QPQ nitrided. I had my MR fully QPQ nitrided when I understood that this process imparted better corrosion resistance the chrome, had a lower coefficient of friction then chrome, and penetrated twice as deep as chrome plate adds to the steel. All great things.
What I learned AFTERWARDS, is that nitriding also increases the fatigue strength of the base material by nearly three times as much. Around 270%. Meaning that with the lower coeficient of friction (especially with lube added) between both a QPQ nitrided barrel/barrel extension and bolt, coupled with the increased fatigue strength of the nitriding process, my nitrided bolt should last an easy 20k rounds or more.
Looks like I need to send my spare off for nitriding as well, and I think that I'm going to start having all of my DI parts nitrided too.
At this point, I can't find a single negative aspect of nitriding gun parts.
Best part is that even a single dip nitride will enhance the base material greatly and it's a cheap process and when done in bulk, doesn't add a whole hell of a lot to the overall cost of a rifle.
If this became part of the TDP for Mil guns, I think they would find the overall performance of the M4/M16 platform increase greatly, with very little cost increase.
Great post and thanks for the measurements.
However, I should note that not all DI bolts are the same. My LMT bolt has undercut lugs (a round radius at the rear of the bolt lugs) and very slightly 'softer' radii than a BCM bolt on a few other angles (lug roots, etc).
Bill Alexander
06-10-12, 09:02
Ok, so in English, will QPQ reduce the impact toughness of a bolt and lead to a shorter round count life or not?
Alloys that create nitrides are typically contain aluminum, chromium, molybdenum and titanium. With this in mind, nitriding works better on metals that contain these metals, but not in excessive amounts as these metals can create very hard and very brittle (especially in the case of aluminum) nitrides that break easily and cause cracks to form. So the real question is at which amounts *will* these nitride creating metals create a situation where the surface loses its impact toughness? There were a lot of "mays" and "mights" in the above post, i'm looking for verifiable data please.
Same question for barrels and barrel extensions.
Also, does not the addition of the nitriding process lower the coefficient of friction between the materials, thusly reducing the stresses between parts? And since hydrogen isn't part of the nitriding process, nor is surface etching, how does your final statment factor into the equation?
In English, you are looking at a very complex system and then asking questions about metallurgy and fatigue analysis. The answer is statistical and dependent upon the bolt alloy, geometry, surface treatment conditions and loading cycles amongst many others. If you want a brief answer I would not use this type of treatment on an AR bolt and you should note that none of the competitors in the recent competitions for the military submitted this. The current TDP precludes the use of CN for bolts specifically for a reason.
I will answer this out of order. You are looking for verifiable data, for a very case specific application. This can only be achieved by an extended series of testing and given the fact that the life is governed by first stage fatigue in a low cycle environment it is not a viable proposition to accelerate the tests. The only recourse is to real time testing to collect the data. In English you need to shoot a minimum of 32 rifles to failure using a certified batch of ammunition. Ideally many more. Your verifiable data costs considerable money. Unless the party concerned is conducting an academic exercise or writing a research paper the existence of the data is of no help as you will have no ability to either access it or duplicate the result.
You have half answered you own question in that you have researched and found that the nitrogen free radicals can work adversely with certain elements. As to the percentages of elements present that will be detrimental to a metal this will depend upon the loading and the geometry as well as the chemistry. Potential micro surface cracks in a 25lb retaining piece that is 8" thick are of little consequence, as an illustration, but such initiation points in a bolt would be detrimental. Bolts are typically, what is generally referred to as surface hardening alloys, in that the carbon content is lower and they are usually used in an application where the surface will be hardened. But they are also higher alloys so in this instance they are not clearly classified.
Barrels, good ones, are CMV through hardening alloys, draw your own conclusions! Dropping the alloy specification can allow a barrel to be effectively CN treated. The manufacturer must determine this. Stainless steel is out and the ability of the nitrogen to combine with the chromium will frequently leave the resulting part more susceptible to corrosion that the virgin part.
Barrel extensions are good if run in isolation. They are a very suitable alloy but must be taken in the as machined form. CN over the existing case hardening is a variable proposition.
To address friction between components, again the information that you are using is case specific example. In this case the tribological results from a controlled standard test. The information should be regarded as indicative of properties that can be achieved. If you can definitively quantify that a CN treated bolt/barrel extension will impose less bending stress on the lugs than a classical case hardened combination, when there is substantial contamination from combustion gasses and also lubricant, either as applied or burnt, then you have the perfect answer.
The comments wrt hydrogen and surface etching were general information and correctly are not pertinent to the direct discussion of CN on alloys. They were related to the consideration of surface treatments by other methods and how problems may occur.
I hope that you realize that I am not being evasive in trying to provide answers it is just that a simple yes or no does not exist. I also hope that you do not think that I am being detrimental to the use of CN. Many parts benefit from this finish but like NiB, Chrome, Nickel and Ionbond it is not a universal fix all. The gun industry has the tendency to "find" a process/lube/finish and then finding a single good application, pounce upon it without any further examination and use it for everything they can throw into the vat. This said I am examining CN QPQ for barrels in one instance and I think that bolt carriers may be another great application. I like NiB for through hardened parts and use both chrome and Ionbond in my products.
Barrels, good ones, are CMV through hardening alloys, draw your own conclusions! Dropping the alloy specification can allow a barrel to be effectively CN treated.
Barrel extensions are good if run in isolation. They are a very suitable alloy but must be taken in the as machined form. CN over the existing case hardening is a variable proposition.
This said I am examining CN QPQ for barrels in one instance and I think that bolt carriers may be another great application. I like NiB for through hardened parts and use both chrome and Ionbond in my products.
Bill,
with 8620 barrel extensions, the QPQ temperature seems to be at odds with the carburize/harden/temper that they normally get.
With QPQ alone, it appears 8620 does not develop sufficient core hardness for strength.
A material like 4140 seems more suitable for through harden + QPQ treatment.
What's your take?
constructor
06-10-12, 14:01
Bill,
with 8620 barrel extensions, the QPQ temperature seems to be at odds with the carburize/harden/temper that they normally get.
With QPQ alone, it appears 8620 does not develop sufficient core hardness for strength.
A material like 4140 seems more suitable for through harden + QPQ treatment.
What's your take?
I'll agree with you. QPQ does not bring the core hardness up high enough to be a stand alone heat treat. IMO the core should be near 50 for toughness without being brittle.
QPQ for barrels is perfect since they are 32-40 as made and then QPQ makes the surface apx 60 for wear resistance.
The 8620 carriers we had were heat treated as normal then went out for melonite, the melonite treatment dropped the surface hardness apx 1 point but gave them a better corrosion resistant finish.
Bill Alexander
06-10-12, 14:23
8620 alloy is not a through hardening grade, rather it is specifically a surface hardening alloy and regardless of wether it is a gas carburize, solution carburize or CN QPQ it is very difficult to develop the core beyond its natural state. The alloy is selected specifically for this reason and the designer must account for this when using such alloys. The ability for the core not to become excessively hard is key but grain growth and inter-granular precipitation of carbides, nitrides must be considered when looking at the heat treatment. Phase diagrams become very important. Remember when considering gun parts fatigue is the dominant failure mode so a hard core may be detrimental
4140 carries more carbon and will through harden. CN-QPQ should be approached with caution or the resulting part may simply become brittle. This is not to preclude such an alloy. Slight alloy alterations may help. For a barrel one must restrain grain growth to prevent loss of ductility over that of the heat treatment. A good hard surface and nice tempered core is of little help if the elongation to break is reduced disproportionately.
It is difficult to examine any material simply in terms of hard or soft, ductile or brittle etc. Fracture toughness is a related but independent property. S-N diagrams are considered for the fatigue, and a material with extremely high tensile yield point may fail rapidly in fracture. In mechanisms there are considerations for strain rate dependancy. The barrel extension is subject to compressional loading under the lugs as well as shear and a bending moment. so compressional strength and galling must be examined.
It is way to easy to let the complexity of material examination become an impenetrable cloud. Once the basics are known, testing becomes a good ally.
In English, you are looking at a very complex system and then asking questions about metallurgy and fatigue analysis. The answer is statistical and dependent upon the bolt alloy, geometry, surface treatment conditions and loading cycles amongst many others. If you want a brief answer I would not use this type of treatment on an AR bolt and you should note that none of the competitors in the recent competitions for the military submitted this. The current TDP precludes the use of CN for bolts specifically for a reason.
I find the last part interesting. When was the specific requirement for no CN added to the TDP? Is it a requirement that's been there since the beginning and simply been a carry-over or was it added later?
I will answer this out of order. You are looking for verifiable data, for a very case specific application. This can only be achieved by an extended series of testing and given the fact that the life is governed by first stage fatigue in a low cycle environment it is not a viable proposition to accelerate the tests. The only recourse is to real time testing to collect the data. In English you need to shoot a minimum of 32 rifles to failure using a certified batch of ammunition. Ideally many more. Your verifiable data costs considerable money. Unless the party concerned is conducting an academic exercise or writing a research paper the existence of the data is of no help as you will have no ability to either access it or duplicate the result.
Exactly. I was hoping that somebody had actually done a test for this data and I didn't know if you were explaining the theory or the data, which is why I asked.
So far from what I'm reading, I should simply shoot the shit out of my nitrided bolt, but keep my non-nitrided bolt handy should the CN bolt fail.
You have half answered you own question in that you have researched and found that the nitrogen free radicals can work adversely with certain elements. As to the percentages of elements present that will be detrimental to a metal this will depend upon the loading and the geometry as well as the chemistry. Potential micro surface cracks in a 25lb retaining piece that is 8" thick are of little consequence, as an illustration, but such initiation points in a bolt would be detrimental. Bolts are typically, what is generally referred to as surface hardening alloys, in that the carbon content is lower and they are usually used in an application where the surface will be hardened. But they are also higher alloys so in this instance they are not clearly classified.
So much of what has been discussed is still clearly in the realm of theory as there have been no actual tests. While the known properties of various materials and processes under other conditions clearly point to *possible* issues in this situation, the fact is that nobody knows for sure and nobody wants to put in the time, effort, and finances to find out.
Barrels, good ones, are CMV through hardening alloys, draw your own conclusions! Dropping the alloy specification can allow a barrel to be effectively CN treated. The manufacturer must determine this. Stainless steel is out and the ability of the nitrogen to combine with the chromium will frequently leave the resulting part more susceptible to corrosion that the virgin part.
The above I knew. So far the only reason I could see for someone to CN stainless is for a color change, but then again, black oxide treatment can do that without compromising the base material.
Barrel extensions are good if run in isolation. They are a very suitable alloy but must be taken in the as machined form. CN over the existing case hardening is a variable proposition.
Interesting. I was under the impression that the temperatures involved in CN-QPQ not only acted as a stress relief for the base metal, but also had no effect on pre-existing case hardening.
I know that case hardening goes deeper then CN, though, so might it be a case of CH preventing CN from penetrating as deep and not getting the full effect from the CN due to the CH?
One would think that in this case, "more is better". Taking information from the bolt discussion above, if a part is case hardened (deeper penetration the CN), and then CN treated, even if the CN were to develop fatigue cracking, wouldn't the CH prevent the cracks in the CN to develop further into the base material? Or does CN remove the CH or destroy its properties?
That being said, wouldn't this also apply to bolts as well?
To address friction between components, again the information that you are using is case specific example. In this case the tribological results from a controlled standard test. The information should be regarded as indicative of properties that can be achieved. If you can definitively quantify that a CN treated bolt/barrel extension will impose less bending stress on the lugs than a classical case hardened combination, when there is substantial contamination from combustion gasses and also lubricant, either as applied or burnt, then you have the perfect answer.
Sorry, that made me laugh. In other words, there is no perfect answer. For all the number crunching and understanding of metallurgy and processes, what happens with the end user simply cannot be accounted for sometimes.
The comments wrt hydrogen and surface etching were general information and correctly are not pertinent to the direct discussion of CN on alloys. They were related to the consideration of surface treatments by other methods and how problems may occur.
Roger that.
I hope that you realize that I am not being evasive in trying to provide answers it is just that a simple yes or no does not exist. I also hope that you do not think that I am being detrimental to the use of CN.
Absolutly not! I just like to understand, and while I have a base knowledge of metallurgy (former DoD shipfitter), the higher end stuff like what we are currently discussing is, other then the homework i've done myself, not fully within my realm of understanding. This is why I ask questions.
I hope my questions didn't come across as "challenging". I just tend to be pretty direct about things when I want to learn.
Many parts benefit from this finish but like NiB, Chrome, Nickel and Ionbond it is not a universal fix all. The gun industry has the tendency to "find" a process/lube/finish and then finding a single good application, pounce upon it without any further examination and use it for everything they can throw into the vat. This said I am examining CN QPQ for barrels in one instance and I think that bolt carriers may be another great application. I like NiB for through hardened parts and use both chrome and Ionbond in my products.
Outstanding information.
Thank you for taking the time to explain things a little further in depth, I appreciate it. I hope you don't mind me asking questions.
constructor
06-10-12, 19:32
The company that carburizies the bolts and carriers we machine brings the core of both up to apx 50 for maximium toughness of the parts. I'm not saying what our exterior is but those 2 parts can be either to hard and brittle or not hard enough.
I've seen some bolts on the market that are so hard they chip at the edges around the cam pin hole and I've seen another brand that (I believe are 8620) are so soft that the lugs compressed. I have cut a carrier from that same company in half with a $9 hacksaw, I'm not sure it was tempered at all.
I would like to see some company Melonite a bolt to see how it holds up ...in their own rifle.:sarcastic:
The company that carburizies the bolts and carriers we machine brings the core of both up to apx 50 for maximium toughness of the parts. I'm not saying what our exterior is but those 2 parts can be either to hard and brittle or not hard enough.
I've seen some bolts on the market that are so hard they chip at the edges around the cam pin hole and I've seen another brand that (I believe are 8620) are so soft that the lugs compressed. I have cut a carrier from that same company in half with a $9 hacksaw, I'm not sure it was tempered at all.
I would like to see some company Melonite a bolt to see how it holds up ...in their own rifle.:sarcastic:
You offer NC DI bolts? If so any feedback so far on expected lifespan?
And for what it's worth, I had my HK416 bolt NC-QPQ treated so i'll be able to give a sample of 1 feedback as time progresses.
So far it's got just under a thousand rounds through it with virtually no visible wear. I know that means nothing for microscopic fatigue cracks that may be forming though.
constructor
06-10-12, 22:52
You offer NC DI bolts? If so any feedback so far on expected lifespan?
And for what it's worth, I had my HK416 bolt NC-QPQ treated so i'll be able to give a sample of 1 feedback as time progresses.
So far it's got just under a thousand rounds through it with virtually no visible wear. I know that means nothing for microscopic fatigue cracks that may be forming though.
We haven't made any in the last year but will get back to it after the move.
Are you taking a completely raw bolt and just having in melonite treated as the ONLY heat treat or was the bolt carburized to begin with by HK and then Melonite treated?
The bolts and carriers we machine are carburized first and then melonite treated or we have had some TIN and TiAlN coated after being heat treated.
I've talked to 2 different companies that heat treat material for us using different processes both have told me Melonite is a quick process so the core never makes it to 10 points under the surface hardness if the material is .125 thick. If it is a very thin piece like a saw blade or an automatic transmission steel then the core will gain depending on the thickness of the material.
I drill though hundreds of Melonite QPQ treated barrels a month, after the surface is broken with a carbide bit the rest of the material is very soft just like cutting through a normal stainless or parkerized CM barrel.
We haven't made any in the last year but will get back to it after the move.
Are you taking a completely raw bolt and just having in melonite treated as the ONLY heat treat or was the bolt carburized to begin with by HK and then Melonite treated?
To be honest, I have no idea how HK treats or processes their bolts. I would assume they have some sort of heat treat process, otherwise their products wouldn't last like they do.
I had one of my HK bolts QPQ nitrided after the fact on top of whatever it was HK did.
The bolts and carriers we machine are carburized first and then melonite treated or we have had some TIN and TiAlN coated after being heat treated.
Any feedback on the carburized/nitrided bolts regarding bolt life, etc.?
I've talked to 2 different companies that heat treat material for us using different processes both have told me Melonite is a quick process so the core never makes it to 10 points under the surface hardness if the material is .125 thick. If it is a very thin piece like a saw blade or an automatic transmission steel then the core will gain depending on the thickness of the material.
I drill though hundreds of Melonite QPQ treated barrels a month, after the surface is broken with a carbide bit the rest of the material is very soft just like cutting through a normal stainless or parkerized CM barrel.
I am aware of the limitations of straight nitriding, which is why I commented on that in my convo with Bill about having a good CH process under nitriding would prevent any possible cracks in nitriding from spreading further.
I would never think it a good idea to forgo CH in favor of straight nitriding.
constructor
06-11-12, 09:27
To be honest, I have no idea how HK treats or processes their bolts. I would assume they have some sort of heat treat process, otherwise their products wouldn't last like they do.
I had one of my HK bolts QPQ nitrided after the fact on top of whatever it was HK did.
Any feedback on the carburized/nitrided bolts regarding bolt life, etc.?
I am aware of the limitations of straight nitriding, which is why I commented on that in my convo with Bill about having a good CH process under nitriding would prevent any possible cracks in nitriding from spreading further.
I would never think it a good idea to forgo CH in favor of straight nitriding.
I don't know about the bolt life we have never had one break.
Agree, carburize first melonite after.
Bill Alexander
06-11-12, 13:42
:rolleyes:
What effect does nickel content have on work hardening and reduction in fatigue life?
Heavy Metal
06-11-12, 14:27
Bill,
The reason Grumpy is so intent on this line of questioning, is he had his HK- MR556 bolt QPQ'd a couple months ago before you made your post yesterday. He is kind of stuck with the results at thsi point.
:rolleyes:
Now that's funny!
Looks like someone jumped both feet in before understanding the complexity of their decision.
Sorry if this has been mentioned already in this thread.
Is there any good data or user experience with JP'S ENHANCED BOLTS? (http://www.jprifles.com/1.4.7_bc.php)
Can't seem to find any long-term or short-term experiences on these. I see some early threads in the '09 time frame of folks that have them, but nothing recent with how they've performed for them.
Found something on ARFCOM about them not being what they used to be - that the supplier changed and now it's all marketing fluff or something.
sinlessorrow
06-11-12, 16:48
nvm didnt see the bolt part
Bill,
The reason Grumpy is so intent on this line of questioning, is he had his HK- MR556 bolt QPQ'd a couple months ago before you made your post yesterday. He is kind of stuck with the results at thsi point.
Exactly.
Some of the stuff Bill has been talking about wasn't something that I could find anywhere, regardless of the countless hours I spent researching nitriding prior to having the process done.
Much of it I did find though, and unfortunatly, most of it, just like Bill himself has said, is a whole lotta "maybes", "mights", "mays", etc. without any hard data, especially end user data or real test data to back it up.
Not poo-pooing what Bill is saying as he has a very firm grasp on the technicals and possibilities, but at the same time, we're once again left in a position where we're lacking empiracle data.
Now that's funny!
Looks like someone jumped both feet in before understanding the complexity of their decision.
I did exactly, that. But to be honest, I'm not too worried about it. The "complexity" of the decision is still left in theory mode as there is no data. I think Constructor would have a better idea of this as he actually sells Nitrided DI bolts and would be in a position to hear enduser feedback if those bolts were demonstrating markedly shorter lifespans then typical DI bolts.
I suppose the questions at that point are: How long has Constructor been selling nitrided bolts for?, Have any customers given positive feedback regarding high round count rifles?, and has he done any testing of his own on his product?
Look, i'm all for trying to understand everything one can about a process before arbitrarily just having it done without thought to possible side effects. I did all the research I could and there was not a lot about this exact topic. So I took the plunge.
At the same time, the information we've gotten on this exact topic from Bill, has been.....less then revealing. Lots of maybes that ultimatly result in "I don't know"s. It's one thing to explain the theory, it's another to have the data. So far, all we have is theory.
If my parts break and don't last, well then i'll be a part of that data and can help someone else in the future. No skin off my back. It's just a bolt.
constructor
06-11-12, 23:17
:rolleyes:
Let me clarify for you Bill.
We had 2 Grendel bolts break because the receiver the Grendel barrel was in was not square. Do you square your receivers Bill?
After we squared the receiver for the Grendel customer he has not broken another bolt. Just never know when a smile is going to bite you in the ass do you?
BTW we may start making Grendel bolts, we have only made 264LBC bolts for the last few years.:D
constructor
06-11-12, 23:40
Exactly.
Some of the stuff Bill has been talking about wasn't something that I could find anywhere, regardless of the countless hours I spent researching nitriding prior to having the process done.
Much of it I did find though, and unfortunatly, most of it, just like Bill himself has said, is a whole lotta "maybes", "mights", "mays", etc. without any hard data, especially end user data or real test data to back it up.
Not poo-pooing what Bill is saying as he has a very firm grasp on the technicals and possibilities, but at the same time, we're once again left in a position where we're lacking empiracle data.
I did exactly, that. But to be honest, I'm not too worried about it. The "complexity" of the decision is still left in theory mode as there is no data. I think Constructor would have a better idea of this as he actually sells Nitrided DI bolts and would be in a position to hear enduser feedback if those bolts were demonstrating markedly shorter lifespans then typical DI bolts.
I suppose the questions at that point are: How long has Constructor been selling nitrided bolts for?, Have any customers given positive feedback regarding high round count rifles?, and has he done any testing of his own on his product?
Look, i'm all for trying to understand everything one can about a process before arbitrarily just having it done without thought to possible side effects. I did all the research I could and there was not a lot about this exact topic. So I took the plunge.
At the same time, the information we've gotten on this exact topic from Bill, has been.....less then revealing. Lots of maybes that ultimatly result in "I don't know"s. It's one thing to explain the theory, it's another to have the data. So far, all we have is theory.
If my parts break and don't last, well then i'll be a part of that data and can help someone else in the future. No skin off my back. It's just a bolt.
Our bolts aren't like most other bolts and I'm not going to post everything I changed on an open forum but it seems like the HK bolt has a few of the same features. Anyone that has one of our bolts can compare it to a mil spec bolt and easily see the changes and should be able to understand the whys. The extra amount of material itself will change the lifespan more than anything if the alloy and heat treat are the same. IMO QPQ does make the surface more corrosion resistant which may slow or prevent the pitting that can be the starting point of stress cracks. QPQ actually softens an already carburized bolt but maybe only 1 point according the the engineer at the plant and 1 point changes the TS or YS very little.
I have never heard of any company doing a test to see how QPQ effects the life of a bolt. From what Burlington told me I can't see it hurting the bolt.
I only tried one batch of apx 280 bolts 3 years ago, all of them were 6.8 bolts so I doubt the round counts on those are very high.
None of the QPQ, TiN or TiAlN coated bolts have been reported broken.
ETA- the only tests I have done were shear strength tests at the lugs. A fixture with the same dia as a barrel extension but solid, bolt under pressure from the recess area same as a cartridge would do. LWRC back when it was Leitner Wise was already using 9310, I had 4 of those 6.8 bolts. I shot a charity 3 gun event in Durango with the 6.8 using a LWRC bolt and ammo loaded with 90gr TNTs as hot as I could load them without blowing primers. 32.5gr of 10X with SSA brass and CCI 41 primers doing just over 3100fps from an 18" barrel. Round count was 170 minimum and I fired a few extra. I think I still have that bolt in a rifle. I believe those loads to be in excess of 65000psi but not near the Hornady 70,000psi proof loads I test bolts with(1 shot only)
Bill Alexander
06-12-12, 10:39
GrumpyM4 my exasperation was not directed towards you. Your questions are reasonable and well phrased.
It would appear that drilling a few holes in barrels trumps a metrology lab and years of experience, I will let the US Army and the few defense contractors I consult to know, so that they can dump all that expensive, but obviously ridiculous, equipment and the staff.
Equally it would appear that fatigue can be analyzed by firing a few overloaded rounds. And there I was thinking that we needed to run pressure equipment to calibrated standards and resonant load machines to examine fatigue.
The error in this thread lies with myself. I was foolish enough to think that a reasonable contribution might be of help. Instead I find that I am being drawn into a squabble more appropriate to TOS, which has more basis in points scoring that factual information. My absence from this forum will commence.
skullworks
06-12-12, 11:18
Bill, I really appreciate your input and contribution to this forum (not to mention this thread in particular)!
constructor
06-12-12, 12:10
GrumpyM4 my exasperation was not directed towards you. Your questions are reasonable and well phrased.
It would appear that drilling a few holes in barrels trumps a metrology lab and years of experience, I will let the US Army and the few defense contractors I consult to know, so that they can dump all that expensive, but obviously ridiculous, equipment and the staff.
Equally it would appear that fatigue can be analyzed by firing a few overloaded rounds. And there I was thinking that we needed to run pressure equipment to calibrated standards and resonant load machines to examine fatigue.
The error in this thread lies with myself. I was foolish enough to think that a reasonable contribution might be of help. Instead I find that I am being drawn into a squabble more appropriate to TOS, which has more basis in points scoring that factual information. My absence from this forum will commence.
So are you saying that the 9310 alloy that LWRC, JP, LMT, Myself and even that you have said in the past that you have your bolts made from is not strong enough for use as bolts in a AR15? Or are you saying the larger radii and more material due to design changes that HK and I have made make the bolts weaker?
The only thing I said was from what I have seen the hundreds of melonite barrels I drill through are a hell of a lot softer on the inside than a 9310 alloy bolt that has been carburized.
The engineers at the companies that actually perform the melonite process told me I would not get the desired results by ONLY melonite treating a 9310 bolt. That is why I have the bolts carburized first and then do what ever treatment after.
So when is the military changing to melonite treated bolts?
sinlessorrow
06-12-12, 12:47
Bill, I really appreciate your input and contribution to this forum (not to mention this thread in particular)!
I agree as well, Bill has made some excellent contributions.
everyusernametaken
06-12-12, 13:16
Same here. Your contribution was meaningful, and a lot of us clearly do appreciate it, even if not actively posting in this thread.
I just come here for the information. Don't want to start fights.
Ok, I got some information regarding wear on the HK bolts in our guns, from the head armorer in the NDLO.
Initially, there were some issues with bolt lugs shearing after a low round count, on some of the first weapons issued.
This was a result of HK changing their steel supplier, and this supplier had some issues with the alloys used and the hardening process. They switched back to the original supplier, and these issues went away.
The warranty on parts life that we have from HK is 10000 rounds, with regards to service intervals. The warranty we have from Colt Canada on the C8's is 6000 rounds.
What they have seen, as far as bolt lugs shearing off, is that it happens on some weapons, depending on firing schedules, after 8-10k rounds. For them, that is acceptable, and they just replace the parts without any more fuss.
I will also concede that I was in error with regards to the unlocking process, and that the unlocking in the DI design is less stressful than the op-rod design, seeing as the op-rod strike is instantaneous, and not gradual.
skullworks
06-15-12, 04:03
Sir, not to go too far off topic, but please let me know what you think of this (it's in Swedish): Funktionsprincip AR-15 (https://docs.google.com/open?id=0B20VYXOOQPQ0NTQ2MGJjYTAtOGM1ZC00ZjFjLWI0NDItYTYwZWI2N2M4Zjhi).
Sir, not to go too far off topic, but please let me know what you think of this (it's in Swedish): Funktionsprincip AR-15 (https://docs.google.com/open?id=0B20VYXOOQPQ0NTQ2MGJjYTAtOGM1ZC00ZjFjLWI0NDItYTYwZWI2N2M4Zjhi).
If you were referring to me, it looked good, both translation and content.
I have seen the original post in english, so to me it looked spot on.
skullworks
06-16-12, 11:00
Clint,
I'm at a stag party right now, but in the opening paragraph there are two hotlinks pointing to the original thread at arf.com. However, there is some additional info that I added to this document to further explain the DI system.
Tatatatatatapatalk 2
skullworks
06-16-12, 21:36
.. in the opening paragraph there are two hotlinks pointing to the original thread at arf.com.
Actually, there was just one link - this: http://www.ar15.com/content/page.html?id=256
Markasaurus
06-19-12, 17:39
I read the first 3 pages including some of the technical analysis post...di vs piston bolt life - ignore it, just buy a stag, either piston or di. Shoot it til the bolt breaks then send it in for a free bolt. Lifetime warranty. Problem solved!
I read the first 3 pages including some of the technical analysis post...di vs piston bolt life - ignore it, just buy a stag, either piston or di. Shoot it til the bolt breaks then send it in for a free bolt. Lifetime warranty. Problem solved!
Yeah good luck with that. Ill stick with the more proven guys.
wow, lot of info
I had an overgassed AR as my demo unit, the bolt had made it about 15k. I shoot primarily crappy ammo so overgassed on that is probably closer to normal operating/unlocking pressures.
I was having some issues with a piston gun so I substituted the DI AR bolt with heavy mileage. It sheared a lug off the top of the bolt very quickly. This upper was having a true bind issue from the oprod. The extension had already been filed to a mouth and it was still getting carrier hits on the sharp edge meaning the carrier was possibly getting near outside the od of the tube.
not real conclusive but there is an additional mode of stress on the bolt lugs for a piston weapon with loser tolerances, if it were nicely supported and no tilt then they would be more equal
Markasaurus
07-19-12, 07:46
I find these technical discussions very interesting. I don't know enough about this except to know i can't comment on bolt life. I have a spare bolt and i own a Stag with lifetime warranty....so with any luck i won't have a bolt problem that will cost me much to fix
skullworks
07-19-12, 16:28
A friend of mine bought a JP CTR-02 about two years back. He's been using it for IPSC Rifle, and during the Nordic Championships this weekend the bolt split into two. The round count is about 7000. $187 later he had a JP EnhancedBolt as a replacement. JP claims a bolt life of 60,000 rounds for these babies. What's your experience? Does anyone have a document round count for one of these bolts that surpass 20k?
A friend of mine bought a JP CTR-02 about two years back. He's been using it for IPSC Rifle, and during the Nordic Championships this weekend the bolt split into two. The round count is about 7000. $187 later he had a JP EnhancedBolt as a replacement. JP claims a bolt life of 60,000 rounds for these babies. What's your experience? Does anyone have a document round count for one of these bolts that surpass 20k?
I asked this same exact question several pages back and never got an answer on JP EnhancedBolt round counts...
skullworks
07-19-12, 16:55
I asked this same exact question several pages back and never got an answer on JP EnhancedBolt round counts...
So you did. Well, now you got a free repeat. ;)
dangertree
07-20-12, 08:47
Yeah good luck with that. Ill stick with the more proven guys.
Stag (as CMT) have been DOD Certified M4/M16 sub-contractors since the early 1970s. They are second only to Colt themselves in length of time producing USGI parts. They manufacture parts for all the top names.
If you think Stag Arms isn't proven, you've been lied to.
sinlessorrow
07-20-12, 09:58
I did find where and why people quote 5-6k for bolt life.
Its what SOCOM has for their replacement schedule, this however is when the bolt develops micro cracks so they replace them just in case. They mentioned this in the SOPMOD 2006 NDIA.
You could probably still get 8-10k out of a bolt with micro cracks though.
@dangertree. Stag is not CMT. That is like saying bushmaster must be as good as remington because they are both cerberus
A friend of mine bought a JP CTR-02 about two years back. He's been using it for IPSC Rifle, and during the Nordic Championships this weekend the bolt split into two. The round count is about 7000. $187 later he had a JP EnhancedBolt as a replacement. JP claims a bolt life of 60,000 rounds for these babies. What's your experience? Does anyone have a document round count for one of these bolts that surpass 20k?
JP says on their webpage that "mil-spec" bolt lives max 6000 rounds and starts cracking by 3000 rounds. And that their bolt is better, because uses better steel. No bolt life claim. But 7000 rounds is more than 6000 for sure, so it is "better".
Here we see different results. Some carbine bolts split in two at around 6000 rounds (do not remember make). On other hand my friends rifle length Stag uses same bolt for over 15000 rounds (rifle seem to be easier on bolts comparing to carbine).
dangertree
07-20-12, 10:16
@dangertree. Stag is not CMT. That is like saying bushmaster must be as good as remington because they are both cerberus
Absolutely untrue.
Stag Arms is the assembly wing of CMT, they are the same parts, same spec, same markings, same everything.
If you think differently, you've been misled, (perhaps by someone trying to sell CMT sourced parts for more than Stag sells for, the main source of info running down Stag, particularly here).
For the stag thing, I've understood it as stag is CMT's storefront brand. I bought one a couple years ago(before I knew better). It has the 4140 barrel, untested barrel and bolt etc... however, I've had about 5k through it without a single malf. Its not a high round count - and is not to the specs of colt/noveske/bcm/dd etc, but for a "midgrade" ar, id say stag and SW are the 2 best of that group (I paid $750 otd). In fact, I've only seen 2 complaints/problems about stag and one was a rediculous round count - guy claimed thousandssSSS of rounds per month. All that said, Im having a top-grade gun put togethe once I get the funds.:)
For the bolt stuff, the LMT bolts in theory should be better with the radiused lugs(where they come out of the bolt). This distributes the stress.
Heat has been shown to be a non issue. Also, on TOS I think they had numbers posted - the carbine gas on a 16" barrel(maybe a 14.5") caused unlocking before the barrel depressurized down to the piston camber pressure levels. In midlengths, it was later reducing a lot of pressure from the lugs.
For the cam pin hole, I would think that a midleth would help in 2 areas. 1- slightly slower cycling which means less stress. 2 - less pressure on bolt from the barrel gas, reducing friction on the lugs, which would reduce stress on the campin hole.
These are just intuitive and not tested by me. Its hard to test since most large organizations use carbine gas.
sinlessorrow
08-18-12, 17:11
I did some talking to Kevin and part of the reason for wanting a FF rail to phase out the M4 RAS was because apparently SOCOM found that it increased reliability and parts life. I would be interested to know their findings, but I am not privilidge to that information. It was explained to me that when you have lights and lasers attached to the M4 RAS and then exert force on the rail it causes the barrel extension to slighty move out of alignment and cause excessive wear and decrease the bolt life.
Magic_Salad0892
08-18-12, 19:09
Exactly...
Shoot it until it breaks.
Or till it hits 10k.
PM could save your life.
Or till it hits 10k.
PM could save your life.
On top of that, if your bolt breaks while firing, couldnt that lead to other parts being damaged? Seems like driving a car till the wheels fall off instead of replacing a fixed axle... way more headache in the long run. Of course, I've never had a bolt break so I really dont know what happens when they fail.
Re: temperature-- the bolt lug difference between piston and Di is about 40*f. The bolt body, around 100*f. Now, this temperature cycle fatiguing the bolt, would it not be much worse if another 50*f were stacked in? Would it then not be logical that an m4 shot in the winter would break the bolt at a different rate by a very noticeable amount of rounds than one shot in the heat of the summer? I just can't believe such a differsnce is measurable.
Re: qpq-- I had the slide on my stainless Sig qpq treated. I also have a stainless Sig that was not. The one that does not, shows self limited peening where the barrel hood impacts the locking interface of the slide, fore of the chamber. The qpq weapon was fired a few hundred times, then sent to be treated. Upon return, and firing it, I note fine chips instead of peebing of the slide. The barrel lug on the other hand, I have to inspect again, but it seems much more suitable. I would not qpq things blindly and expect positive returns in all cases.
sinlessorrow
08-19-12, 15:00
Re: temperature-- the bolt lug difference between piston and Di is about 40*f. The bolt body, around 100*f. Now, this temperature cycle fatiguing the bolt, would it not be much worse if another 50*f were stacked in? Would it then not be logical that an m4 shot in the winter would break the bolt at a different rate by a very noticeable amount of rounds than one shot in the heat of the summer? I just can't believe such a differsnce is measurable.
Re: qpq-- I had the slide on my stainless Sig qpq treated. I also have a stainless Sig that was not. The one that does not, shows self limited peening where the barrel hood impacts the locking interface of the slide, fore of the chamber. The qpq weapon was fired a few hundred times, then sent to be treated. Upon return, and firing it, I note fine chips instead of peebing of the slide. The barrel lug on the other hand, I have to inspect again, but it seems much more suitable. I would not qpq things blindly and expect positive returns in all cases.
Excellent point, if the extra heat from DI is what killed the bolt, then rifles used in very cold places would have incredibly shorter lifes than ones used in warmer temps. Since the heating/cooling cycle would be far greater.
On the cold temp issue, the HK416 initially had problems in nordic conditions. I wonder if that was a bolt issue.
What problems was the HK having in "nordic" conditions?
dangertree
08-19-12, 20:56
For the stag thing, I've understood it as stag is CMT's storefront brand. I bought one a couple years ago(before I knew better). It has the 4140 barrel, untested barrel and bolt etc... however, I've had about 5k through it without a single malf. Its not a high round count - and is not to the specs of colt/noveske/bcm/dd etc, but for a "midgrade" ar, id say stag and SW are the 2 best of that group (I paid $750 otd). In fact, I've only seen 2 complaints/problems about stag and one was a rediculous round count - guy claimed thousandssSSS of rounds per month. All that said, Im having a top-grade gun put togethe once I get the funds.:)
Stag Arms parts are the equal in real quality to say, Colt or BCM, and better than most. For complete rifles, the 4140 1/9 Chrome Lined compares to well to other 1/9 4140 barrels, and cost less than the 4150 1/7. I personally own both with plenty down the pipes. Because they market a rifle with a 4140 barrel option, doesn't a bad manufacturer make. Lots of people are well served with a 1/9, and theirs (mine) measures out to 1/8.25", which has no issues with 1/7, regardless of conditions. When I burst a semi-auto barrel I'll let you know. Most of my guns are 1/7 4150 though, just because.
For the bolt stuff, the LMT bolts in theory should be better with the radiused lugs(where they come out of the bolt). This distributes the stress.
Heat has been shown to be a non issue. Also, on TOS I think they had numbers posted - the carbine gas on a 16" barrel(maybe a 14.5") caused unlocking before the barrel depressurized down to the piston camber pressure levels. In midlengths, it was later reducing a lot of pressure from the lugs.
For the cam pin hole, I would think that a midleth would help in 2 areas. 1- slightly slower cycling which means less stress. 2 - less pressure on bolt from the barrel gas, reducing friction on the lugs, which would reduce stress on the campin hole.
These are just intuitive and not tested by me. Its hard to test since most large organizations use carbine gas.
All interesting in theory, but when a rifle has to work in 'adverse', the carbine length will go bang for longer with a wider variety of ammo. As one national armorer employee remarked on the request, 'but carbine length works!'.
The comparison might = searching for flysh!t in pepper however. :haha: They both work well for the vast majority of users.
For myself, carbine length gas + a matched buffer for the stock of ammo. If a carbine runs a H2 with M855, do it. Definitely for MK262. If you've got a flat of Rem white box 223R1, maybe take it down a notch to the H1 or Standard, as works. A H will run everything smoothly but the 77gn high pressure cartridges, which deserve a H2.
BufordTJustice
08-20-12, 03:33
Stag Arms parts are the equal in real quality to say, Colt or BCM, and better than most. For complete rifles, the 4140 1/9 Chrome Lined compares to well to other 1/9 4140 barrels, and cost less than the 4150 1/7. I personally own both with plenty down the pipes. Because they market a rifle with a 4140 barrel option, doesn't a bad manufacturer make. Lots of people are well served with a 1/9, and theirs (mine) measures out to 1/8.25", which has no issues with 1/7, regardless of conditions. When I burst a semi-auto barrel I'll let you know. Most of my guns are 1/7 4150 though, just because.
I'm going to have to ask you to provide documentation supporting this statement.
All interesting in theory, but when a rifle has to work in 'adverse', the carbine length will go bang for longer with a wider variety of ammo. As one national armorer employee remarked on the request, 'but carbine length works!'.
I'm going to have to ask you to provide documentation supporting this statement.
Further, you are simply assuming that the increased friction from the buildup of 'crud' is the reason that a rifle may not 'work' in an adverse condition. I run rifles with the BCG's bearing surfaces polished to a shine and dripping with quality lube (Slip 2k EWL)....friction is not an issue for me even after thousands of rounds with no cleaning.
Acknowledging that overcoming friction is not a primary factor in reliability, the 16" carbine gas system has only liabilities in its corner. I think that you have not taken into account the greatly increased gas port pressure (and correlating increased stresses on the bolt, cam pin, and extractor) in a 16" carbine gas system vice a 16" mid length gas system. Add to that the increase in dwell time (time system is under gas pressure) and you have a compounding of issues that ALL work to only degrade bolt life and extractor performance at an accelerated rate over the 16" midlength gas system. Pat Rogers put over 46,000 rounds through his "Filthy 14" BCM 16" mid-length before retiring it....under a rigorous class schedule, to boot. You show me a 16" carbine-gas Stag/CMT gun that has done that, and we can begin to have a factual conversation about this topic.
skullworks
08-20-12, 03:49
Stag Arms parts are the equal in real quality to say, Colt or BCM, and better than most...
Stag bolt cam pin after less than 500 rounds fired. This is the third Stag cam pin I know of that has cracked like this after less than 1000 rounds fired. Equal my a**!
https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-ash4/404094_482303738446698_637264883_n.jpg
What problems was the HK having in "nordic" conditions?
You do not know? It was all over The Internet that HK does not work in Norway*. Have you ever been in Norway? This is one hell of cold country you know! :secret:
* for some one particular poor SOB with Internet access.
skullworks
08-20-12, 07:06
Since Arctic1 has some personal experience of the HK in not only Nordic, but Norwegian climate I guess he was wondering what the rumour mill had cooked up this time. ;)
sinlessorrow
08-20-12, 07:11
Since Arctic1 has some personal experience of the HK in not only Nordic, but Norwegian climate I guess he was wondering what the rumour mill had cooked up this time. ;)
It's probably that one report from the guy who had a bad experience, certainly doesn't mean everyone had the same as him. From what I can remember it is the equivelant to our 507th maint.
Since Arctic1 has some personal experience of the HK in not only Nordic, but Norwegian climate I guess he was wondering what the rumour mill had cooked up this time. ;)
Same rumour as before. Poor SOB came from deep freezing outdoors to hot indoors with his rifle. Let it accumulate moisture everywhere. Then he went outdoors again and let rifle freeze on him. Then he blamed the rifle.
You do not do that with selfloader in arctic condition. Not with HK416, not with M16, not with M4, not with G3. Not even with AK (while AK is little more forgiving and you can kick charging handle). At least this is what someone who spent some time in arctic conditions told me.
Stag Arms parts are the equal in real quality to say, Colt or BCM, and better than most.I'll politely disagree. Stag is a perfectly suitable rifle for a budget conscious enthusiast, but they're not a mil-spec machine, nor would I be comfortable staking my life or the lives of my officers on one, at least not to the extent I do my DD and my Colt.
I don't know of anyone who has ever had to fire a weapon in anger, LE or Armed Forces alike, who carries a Stag...
All interesting in theory, but when a rifle has to work in 'adverse', the carbine length will go bang for longer with a wider variety of ammo. As one national armorer employee remarked on the request, 'but carbine length works!'.
No it won't. As illustrated during the development of Mk 262 ammo. The carbine chamber pressures became excessive and caused extraction issues during extended firing cycles.
A longer gas system with a lower port pressure will allow more time for the chamber pressures to lower before extraction.
The issues we have seen in the cold are a result of poor/improper cold weather maintenance, and not particular to that weapon system.
And it is not a bolt issue. :confused:
There have been a few incidents where internals have frozen; safety, charging handle etc, rendering the weapon inoperable, though with an easy enough fix.
However, if proper cold weather maintenance is enforced by leaders, these problems do not occur; use lube, remove water/moisture during field cleaning, use lube, remove snow with the issued snow removing brush (for clothes, but it works), use lube, avoid moving the weapon from cold, to hot, to cold again if possible, keep weapons covered when not in use to protect from elements, use lube....oh, and use lube.
It was most prominent with mechanized infantry who were continously dismounting, mounting and dismounting their IFV's.
It also happens with MG-3's, M2 Brownings, Glocks etc etc.....I actually had my pistol freeze in my holster once, could not get it out until the holster thawed. It was a Safariland 6004.
I have seen the picture in post #44 of the HK416 feedback thread, as well as the post by the norwegian soldier over on TOS. That single post led to an article on the Firearms blog, stating the the norwegians had issues with their guns in the cold weather. Great reporting and source verification/use. :rolleyes: Especially seeeing as the post was made only a few months after general issue started. My unit was the first to get it, May 2008. The rest started to have it issued in August 2008, and service-wide fielding was complete sometime in 2010 I think.
It is safe to say that many of the "issues" arriving are not due to weapon design or quality, but a lack of institutional knowledge on the platform. It's only been in service for 4 years, replacing a weapon that had been in service for 40 years. I imagine that the same stuff would appear if US forces switched to an AK or another type of platform they were unfamiliar with.
dangertree
08-20-12, 19:36
I'll politely disagree. Stag is a perfectly suitable rifle for a budget conscious enthusiast, but they're not a mil-spec machine, nor would I be comfortable staking my life or the lives of my officers on one, at least not to the extent I do my DD and my Colt.
I don't know of anyone who has ever had to fire a weapon in anger, LE or Armed Forces alike, who carries a Stag...
Well, again, I disagree, because I do know people who have used Stag Arms rifles in combat.
In Canada anyway, Stag Arms Lefties are in use by high-speed low-drag CF elements, and after hard service in Afghanistan were written up and approved for further purchase. Lefty assaulters with 12.5" supressed guns, love not being gassed out of a fight after one mag (not my words). They have not reported any problems that I know of.
Are you basing this opinion you hold, that Stag Arms are inferior (for unmentioned reasons) to a similarly configured Colt based on personal experience with Stag Arms?
dangertree
08-20-12, 19:43
No it won't. As illustrated during the development of Mk 262 ammo. The carbine chamber pressures became excessive and caused extraction issues during extended firing cycles.
A longer gas system with a lower port pressure will allow more time for the chamber pressures to lower before extraction.
I have not experienced extraction issues on well running carbines with Mk262.
I was referring to filth & corruption from hard use and firing cycles as adverse, rather than extraction. The lower pressure is the point I was making (when it HAS to work).
BufordTJustice
08-20-12, 20:46
I have not experienced extraction issues on well running carbines with Mk262.
I was referring to filth & corruption from hard use and firing cycles as adverse, rather than extraction. The lower pressure is the point I was making (when it HAS to work).
So, by your logic, the rifle gas system would be the least reliable because it has the lowest port pressure and the least amount of excess gas. Yet, it is the most reliable...:rolleyes:
Sent from my Samsung Galaxy Epic 4G Touch
BufordTJustice
08-20-12, 20:53
Well, again, I disagree, because I do know people who have used Stag Arms rifles in combat.
In Canada anyway, Stag Arms Lefties are in use by high-speed low-drag CF elements, and after hard service in Afghanistan were written up and approved for further purchase. Lefty assaulters with 12.5" supressed guns, love not being gassed out of a fight after one mag (not my words). They have not reported any problems that I know of.
Are you basing this opinion you hold, that Stag Arms are inferior (for unmentioned reasons) to a similarly configured Colt based on personal experience with Stag Arms?
I know a US SF guy who used a Bushmaster in combat......before he knew better. Plenty of the SWAT guys in my agency use Bushmaster. They also have constant issues and have to resort to using the d-ring to maintain enough extractor tension.
This does not mean I will be running out and buying a bushmaster any time soon.
Sent from my Samsung Galaxy Epic 4G Touch
dangertree
08-20-12, 22:07
I know a US SF guy who used a Bushmaster in combat......before he knew better. Plenty of the SWAT guys in my agency use Bushmaster. They also have constant issues and have to resort to using the d-ring to maintain enough extractor tension.
This does not mean I will be running out and buying a bushmaster any time soon.
Sent from my Samsung Galaxy Epic 4G Touch
OK. But what does Bushmaster have to do with this?
BufordTJustice
08-20-12, 22:24
OK. But what does Bushmaster have to do with this?
They also have a ton of fanboys who used to claim 'as good as' status when compared to manufacturers like Colt, LMT, bcm, DD, etc. If you use the search button, you'll find plenty of people saying as good as......and even more coming here with problems. Do a search for stag issues and you'll find the same.
Further, it's not incumbent to me to accept your argument. It's incumbent upon you to support it with facts. Starting with stags' full compliance with the TDP, and including multiple high round count tests under rigorous conditions. Like Pat Rogers using BCM in his training classes.
Sent from my Samsung Galaxy Epic 4G Touch
I have not experienced extraction issues on well running carbines with Mk262.
This was during the development of the load. The high pressure of the carbine gas system combined with a live round that sat in a 200-300 degree chamber during a lull in shooting would cause some extraction issues.
They (blackhills) had to work the load around the limits of the carbine gas system.
Magic_Salad0892
08-21-12, 09:43
I'm dying to know what SF unit issued a BM...
sinlessorrow
08-21-12, 10:21
I'm dying to know what SF unit issued a BM...
It could only be the SEAL team six cause they get the best.
because I do know people who have used Stag Arms rifles in combat.
Emphasis mine, can we all PLEASE stop mistaking this as a valid pivot-point on which to hinge an assertion meant to be anything other than anecdotal?
It matches my own personal assertion that there hasn't ever been a produced-in-numbers lefty AR from any vendor that hasn't been a soup sandwich....
...in that each (conflicting) assertion is functionally worthless without something besides a desire to be "right" to support it without documentation. We all know people; that's not unique, nor is knowing people that have used stuff in combat in the last decade or so.
Let's move it back to talking about bolt life considerations, per the thread's title, and not yet another "less-filling/tastes-great" mess regarding whole guns and their respective roll-marks.
Please note that there is a difference between pushing the bolt forward so that is has NO contact with the BE lugs and pushing it forward so it has LESS pressure during contact with the BE lugs. What I am saying is that the DI system pushes the bolt forward so that it has LESS pressure on the lugs during contact than when rotated in a piston system. Therefore less stress is incurred on the bolt and BE lugs in a DI system than in a piston system, whereby the bolt life should be longer in a DI system (from a purely mechanical standpoint).
The only way the pressure inside the carrier can push the bolt forward any appreciable degree is if the pressure wave enters the carrier after the pressure in the bore has dropped to near atmospheric
Rogers and Caputo stated on LF that TDP bolts rarely fail at the cam pin. Normally they shed the lugs next to the extractor and the failure is discovered during maintenance.
The goal should be a 20,000 round barrel and bolt life. Replace both at once.
Rogers and Caputo stated on LF that TDP bolts rarely fail at the cam pin. Normally they shed the lugs next to the extractor and the failure is discovered during maintenance.
The goal should be a 20,000 round barrel and bolt life. Replace both at once.
20k rounds for a USGI milspec bolt? Where do you get this info?
The goal for the PIP, not current life expectancy.
sinlessorrow
08-21-12, 13:16
The goal for the PIP, not current life expectancy.
SOCOM was replacing bolts at 6,000 in 2006 with harsh firing schedules. This was before they broke so they could have maybe gone another 2,000. They also noted you can ge 10,000 out of a bolt used under normal schedules, so if a FF rail increases bolt life and they get one made of different materials i can see 10,000+ on harsh schedules and 20,000 under normal ones.
Normally they shed the lugs next to the extractor and the failure is discovered during maintenance.
Yep... here's the conclusions from a report I saw some place...
Failure Analysis of the M16 Rifle Bolt
V.Y. Yu*, J.G. Kohl, R.A. Crapanzano, M.W. Davies, A.G. Elam, M.K. Veach
Department of Civil and Mechanical Engineering
United States Military Academy
West Point, NY 10996, USA
4. Conclusions
The fracture of the M16 bolt resulted from a cumulative effect of high stress concentrations at the fillet radius and the additional stress concentration imposed by the presence of localized pitting at the surface. The bolt possesses many fillet regions which impose numerous areas of high stress concentration. In particular, two fillets experienced higher stress immediately adjacent to the round extractor due to the non-contiguous feature of the bolt. These two specific areas of high stress concentration also corresponded to the same location where failure of the bolt occurred in all fractured bolt specimens. Micrographs obtained from the scanning electron microscope of the fractured surface showed localized pitting at the failure initiation site. In addition, transgranular crack propagation near the pit formations in the fillet regions was observed. The localized pits formed near the locking lugs also served as high stress concentration points. The presence of pits in the material amplified the stresses of the bolt in the locking lug region which already had a high stress concentration due to the irregular geometry of the bolt. This cumulative stress concentration provides a good indicator why the crack initiated and propagated from this region.
The wear observed in the controlled experiment indicates the mechanism of why the corrosion pits formed near the locking lug fillet by exposing the Carpenter Steel 158 base metal to the environment. Vickers microhardness readings near the fillet region show that the bolt was not uniformly case hardened. Comparison of the microhardness readings near the fillet region and 10 mm from this region show a disparity of approximately 100 units. The softer, less carburized region near the fillet contributes to the formation of a wear area after firing just 1800 rounds.
5. Acknowledgements
The authors would like to thank Mr. Victor K. Champagne, Jr. and the Materials Analysis Group at the Army Research Laboratory in Aberdeen Proving Grounds, MD for helpful discussions and for performing SEM work.
6. References
[1] Three-dimensional Pro-Engineer® model of M16 bolt from U.S. Army Testing and Armament Command, Rock Island, IL.
[2] Individual Weapon Systems & 3-D Technical Data Development Team, U.S. Army Testing and Armament Command, Rock Island, IL.
[3] Alloy data Carpenter No. 158® Alloy, Carpenter Technology Corporation, 1981.
sinlessorrow
08-21-12, 14:54
Yep... here's the conclusions from a report I saw some place...
Failure Analysis of the M16 Rifle Bolt
V.Y. Yu*, J.G. Kohl, R.A. Crapanzano, M.W. Davies, A.G. Elam, M.K. Veach
Department of Civil and Mechanical Engineering
United States Military Academy
West Point, NY 10996, USA
Makes me wonder how long a bolt with a finish that can resist the corrosion and lugs that with stress evenly distributed would last.
Yeah... I wonder how hard chroming would have impacted the test.
In any case.. it's a good reason to keep the bolt well lubed.
sinlessorrow
08-21-12, 15:17
Yeah... I wonder how hard chroming would have impacted the test.
In any case.. it's a good reason to keep the bolt well lubed.
Wasnt the original M16 carrier and bolt hard chrime?
I'll politely disagree. Stag is a perfectly suitable rifle for a budget conscious enthusiast, ..
They are a 'plinker grade' rifle.
http://www.thefirearmblog.com/blog/2009/03/06/norwegian-soldiers-having-problems-with-hk416-2/
sinlessorrow
08-21-12, 15:33
http://www.thefirearmblog.com/blog/2009/03/06/norwegian-soldiers-having-problems-with-hk416-2/
That was fixed a while ago.
That was fixed a while ago.
And problem was actually with user, not weapon. Arctic1 wrote it like 1000 times here.
http://www.thefirearmblog.com/blog/2009/03/06/norwegian-soldiers-having-problems-with-hk416-2/
Like I wrote here:
http://m4carbine.net/showpost.php?p=1374161&postcount=134
that is a really poor article, demonstrated by the author referencing a single thread on TOS, where one user has issues.
If stuff like that is taken as gospel, then no wonder the HK got a bad rep. Other issues are described here:
https://www.m4carbine.net/showthread.php?t=92876&page=4
Back to the bolt life discussion.
BufordTJustice
08-21-12, 16:34
I'm dying to know what SF unit issued a BM...
Magic...not issued. The guy brought his own. Yes some are allowed to do that. Others simply do it without asking.
Sent from my Samsung Galaxy Epic 4G Touch
Magic_Salad0892
08-21-12, 20:34
Magic...not issued. The guy brought his own. Yes some are allowed to do that. Others simply do it without asking.
Sent from my Samsung Galaxy Epic 4G Touch
That makes sense. I've seen pics of a few dudes with personal uppers.
BufordTJustice
08-21-12, 20:53
That makes sense. I've seen pics of a few dudes with personal uppers.
Yeah. He runs BCM now (shocker). He's very open about explaining that his BCM 14.5" middy is twice the gun (smoother shooting, more accurate, etc.) that his Bushy was and that he would have had a BCM with him if he knew anything about BCM or about the deficiencies of cheaper manufacturers. So goes life.
Magic_Salad0892
08-21-12, 21:19
Yeah. He runs BCM now (shocker). He's very open about explaining that his BCM 14.5" middy is twice the gun (smoother shooting, more accurate, etc.) that his Bushy was and that he would have had a BCM with him if he knew anything about BCM or about the deficiencies of cheaper manufacturers. So goes life.
How easy is it for dudes in the .mil to get personal uppers issued to them in the field?
dangertree
08-21-12, 21:44
They are a 'plinker grade' rifle.
Could you elaborate on your experience or reasoning leading to your conclusion?
BufordTJustice
08-21-12, 21:46
How easy is it for dudes in the .mil to get personal uppers issued to them in the field?
I couldn't say. He was pretty deep into things....so he didn't have to play by the normal rules of Big Green. His unit was small and used Mk262 almost exclusively, as an example. He was pretty sheepish when I asked him how many of his supervisors were aware of such goings-on. I got the impression that a blind eye was turned. Can't say for sure though....and the vast majority of his activities he can't talk about. His experience is certainly not typical.
*****************************************
Back on topic though. I was looking at pictures of the KAC SR15 E3 bolt and I noticed a few things:
1) the bolt face is fully supported (the interior of the extractor is scalloped-out to accommodate this).
2) the KAC cam pin is tapered/stepped since their bolt has a smaller cam-pin hole in it than a standard mil spec bolt (more material)
3) The bolt lugs are obviously radiused and more substantial
4) The material is apparently different than Carpenter 158-A steel.
These all seem to indicate what the failure modes of a std bolt are....and is consistent with what I'm reading in this thread. Comments?
These are not my pictures...so I'm not taking credit for them.
KAC Bolt:
http://i238.photobucket.com/albums/ff225/deliriou5/KAC_Bolt_LMT_Ecarrier.jpg
http://i238.photobucket.com/albums/ff225/deliriou5/KAC_Bolt_Barrel_extension2.jpg
http://i238.photobucket.com/albums/ff225/deliriou5/KAC_Bolt_Barrel_extension.jpg
dangertree
08-21-12, 22:08
They also have a ton of fanboys who used to claim 'as good as' status when compared to manufacturers like Colt, LMT, bcm, DD, etc. If you use the search button, you'll find plenty of people saying as good as......and even more coming here with problems. Do a search for stag issues and you'll find the same.
I submit to you that CMT/STAG makes a better rifle than Bushmaster, and still don't see the comparison. I compare them to Colt, and their parts are for my purposes, straight milspec and perform well.
Further, it's not incumbent to me to accept your argument. It's incumbent upon you to support it with facts. Starting with stags' full compliance with the TDP, and including multiple high round count tests under rigorous conditions. Like Pat Rogers using BCM in his training classes.
It is perfectly fine for you to accept, or not, anything I say. If you are telling me problems exist with Stag Arms that don't in my experience, I'll just say so.
I think I covered the multiple high round count tests under rigorous conditions question about as much as I will. The carbines are owned by the Crown, not personal use.
I submit to you that CMT/STAG makes a better rifle than Bushmaster, and still don't see the comparison. I compare them to Colt, and their parts are for my purposes, straight milspec and perform well.
It is perfectly fine for you to accept, or not, anything I say. If you are telling me problems exist with Stag Arms that don't in my experience, I'll just say so.
I think I covered the multiple high round count tests under rigorous conditions question about as much as I will. The carbines are owned by the Crown, not personal use.
CMT is stag(I agree stag>BM).
cmt provides many parts to many companies.
I have no clue but this is an examle.
stag uses cmt bolts. so does bcm(again - this is not a fact, its an example that I have no imformation about).
last I knew stag does not test - mine is not anyway.
bcm tests each individual bolt, hpt and mp test. Then they are assembled correctly.
There are some dpms guns that can hang with colt and the bunch, but its not the norm. I will say again, for a mid-level gun, stag and m&P are the top of that group, but comparing what they offer vs bcm/colt, etc shows stag to be lower quality.
bolt material, testing, barrel material, QC, proper assembly, QA - ALL this means you get a better gun at a higher price. Stag does not tear down 10 guns, mix them up, reassemble them randomly and test fire... colt does - hence the trust and higher price.
There is nothing else to say. Stag is good, colt/bcm/lmt/larue/kac are all better(in general). No question.
Edit - There are people here who USE these for a living - for their life. I dont mean your average soldier at boot camp - I mean people who push thier equiptment and selves to the limit constantly. Its what they do. When someone like that uses a specific group of brands, its not because they read it online. They have real experience. I, personally take notice, and copy that. Whether its at a match, sqeezing off on a coyote, or -God forbid- I need to defend myself in my home... I know what I have has been fully vetted to be top of the line and as dependable as anything made by a human can be.
BTW stag is not milspec.
4140 bbl
1/9 twist
any of the inhouse testing...
ANYWAY, back to op about ar vs piston guns. A point I dont remember seeing, look at the ak bolt. 2 Big, fat lugs. ar has many thin lugs so if the stress is not evenly distributed, there will be a shorter life. I dont see this as a detriment, personally. It just comes with the beast. Just some cars take transmission flushes at different intervals.
BufordTJustice
08-21-12, 22:59
I submit to you that CMT/STAG makes a better rifle than Bushmaster, and still don't see the comparison. I compare them to Colt, and their parts are for my purposes, straight milspec and perform well.
It is perfectly fine for you to accept, or not, anything I say. If you are telling me problems exist with Stag Arms that don't in my experience, I'll just say so.
I think I covered the multiple high round count tests under rigorous conditions question about as much as I will. The carbines are owned by the Crown, not personal use.
If you are serious about being taken seriously here at M4C, you'll support your assertions with documentation that Stag/CMT are in full compliance with the TDP. You have submitted no third-party data about CMT/Stag reliability that is on-par with Pat Roger's continual usage of BCM carbines or his 'Filthy 14' in particular.
It's Put-up-or-shut-up time.
I'm not saying you're wrong. I'm saying that if you show facts to support your argument, I'll believe you. Not before then.
dangertree
08-21-12, 23:19
If you are serious about being taken seriously here at M4C, you'll support your assertions with documentation that Stag/CMT are in full compliance with the TDP. You have submitted no third-party data about CMT/Stag reliability that is on-par with Pat Roger's continual usage of BCM carbines or his 'Filthy 14' in particular.
It's Put-up-or-shut-up time.
I'm not saying you're wrong. I'm saying that if you show facts to support your argument, I'll believe you. Not before then.
I appreciate that you're not saying I'm wrong. :D
vicious_cb
08-22-12, 01:16
I couldn't say. He was pretty deep into things....so he didn't have to play by the normal rules of Big Green. His unit was small and used Mk262 almost exclusively, as an example. He was pretty sheepish when I asked him how many of his supervisors were aware of such goings-on. I got the impression that a blind eye was turned. Can't say for sure though....and the vast majority of his activities he can't talk about. His experience is certainly not typical.
*****************************************
Back on topic though. I was looking at pictures of the KAC SR15 E3 bolt and I noticed a few things:
1) the bolt face is fully supported (the interior of the extractor is scalloped-out to accommodate this).
2) the KAC cam pin is tapered/stepped since their bolt has a smaller cam-pin hole in it than a standard mil spec bolt (more material)
3) The bolt lugs are obviously radiused and more substantial
4) The material is apparently different than Carpenter 158-A steel.
These all seem to indicate what the failure modes of a std bolt are....and is consistent with what I'm reading in this thread. Comments?
These are not my pictures...so I'm not taking credit for them.
KAC Bolt:
http://i238.photobucket.com/albums/ff225/deliriou5/KAC_Bolt_LMT_Ecarrier.jpg
http://i238.photobucket.com/albums/ff225/deliriou5/KAC_Bolt_Barrel_extension2.jpg[/IMG]
[IMG]http://i238.photobucket.com/albums/ff225/deliriou5/KAC_Bolt_Barrel_extension.jpg
Now the question is, why are you running your BCG so dry? :)
BufordTJustice
08-22-12, 01:31
Now the question is, why are you running your BCG so dry? :)
This is not my gun. They are not my pix. They belong to a user (whose name I cannot recall) over at TOS.
One day, I will own an SR15 E3 with the URX III smooth-rail. But that day will not be anytime soon. :(
HA! They do not belong to a user on TOS! :D
I posted these pics in my malfunction thread - they were taken after 900+ rounds of which a majority were suppressed and no additional lube was added for the purpose of vetting my upper.
see thread here ==> https://www.m4carbine.net/showthread.php?t=109136
HA! They do not belong to a user on TOS! :D
I posted these pics in my malfunction thread - they were taken after 900+ rounds of which a majority were suppressed and no additional lube was added for the purpose of vetting my upper.
see thread here ==> https://www.m4carbine.net/showthread.php?t=109136
TOS pirates alot of M4C's pics, i've been victim of it before.
That's ridiculous!
So some douche is claiming them as his own? :confused:
BufordTJustice
08-23-12, 04:51
HA! They do not belong to a user on TOS! :D
I posted these pics in my malfunction thread - they were taken after 900+ rounds of which a majority were suppressed and no additional lube was added for the purpose of vetting my upper.
see thread here ==> https://www.m4carbine.net/showthread.php?t=109136
I stand corrected, sir. I just didn't want anybody to think that I was trying to take credit for them.
Thanks for the pix. :D
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.