View Full Version : Hopefully this will be the ultimate bolt life discussion thread...
Since last year i built my first AR, I learned a lot regarding the bolt...
IMO, most people wish for a cost-effective solution that "lasts really long" and is not "virtually indestructible and unobtainium", so it's not limited to a few that's willing to pay. We can get the latter, and probably already did, but maybe not the former. ( "https://www.gunsandammo.com/editorial/surefire-optimized-and-lmt-enhanced-bolt-carrier/360796")
Lewis once told me, "I can make a bolt for an AR-15 that I can guarantee would never break. Unfortunately, it would cost more than the rest of the rifle."
I think the #1 issue is information asymmetry, where we hear bits & pieces all over the web, but none was enough to tell the whole story. You need to have the correct info to make good decisions. Unfortunately, the firearm community are based on experience, not knowledge. Same for both users and companies. Can't address a non-exist problem or go with a flimsy fix, right?
#2 is your average Joe doesn't have enough resources to test it out. That means at least 10,000 rounds or more are fired in a rapid session. To manufacturers, a simple idea could cost even more to iron out, and God only knows if it'll work. How many companies are willing to sell a cheap & effective bolt at a loss?
Let alone those who make it will protect their secrets right away.
Above all else, if a bolt lasts until the gun needs to be fixed (like a rebarrel), at least that doesn't hurt the combat effectiveness, so most are still rolling with their mil-spec bolt. The need isn't there. Those who are looking for an enhancement are going a step further.
On the bright side, though, I think it's doable. We should have enough knowledge regarding bolt design. We just need to know how.
constructor
07-24-23, 21:03
Since last year i built my first AR, I learned a lot regarding the bolt...
IMO, most people wish for a cost-effective solution that "lasts really long" and is not "virtually indestructible and unobtainium", so it's not limited to a few that's willing to pay. We can get the latter, and probably already did, but maybe not the former. ( "https://www.gunsandammo.com/editorial/surefire-optimized-and-lmt-enhanced-bolt-carrier/360796")
I think the #1 issue is information asymmetry, where we hear bits & pieces all over the web, but none was enough to tell the whole story. You need to have the correct info to make good decisions. Unfortunately, the firearm community are based on experience, not knowledge. Same for both users and companies. Can't address a non-exist problem or go with a flimsy fix, right?
#2 is your average Joe doesn't have enough resources to test it out. That means at least 10,000 rounds or more are fired in a rapid session. To manufacturers, a simple idea could cost even more to iron out, and God only knows if it'll work. How many companies are willing to sell a cheap & effective bolt at a loss?
Let alone those who make it will protect their secrets right away.
Above all else, if a bolt lasts until the gun needs to be fixed (like a rebarrel), at least that doesn't hurt the combat effectiveness, so most are still rolling with their mil-spec bolt. The need isn't there. Those who are looking for an enhancement are going a step further.
On the bright side, though, I think it's doable. We should have enough knowledge regarding bolt design. We just need to know how.
It was done 13 years ago, and could have been done several different ways. I'm not sure if Knights E3 was first or LWRC or LMT for the 5.56 bolt. I did it for a different reason, Grendel bolts were breaking and I wanted to use an even larger cartridge the 6BRX. The better longer lasting bolts were offered some near $100 and some around $155 but most will just buy the cheapest bolt possible and complain when it breaks or replace it and move on.
You know how fluidmaster makes the toilet flappers fail after being in the water so long so they can sell more flappers over and over? Most older people are pissed because things aren't built to last anymore, not the common gunowner. If given the choice I think they will buy the cheapest over the best 90% of the time. I'm sure available funds plays a part in that.
Since last year i built my first AR, I learned a lot regarding the bolt...
IMO, most people wish for a cost-effective solution that "lasts really long" and is not "virtually indestructible and unobtainium", so it's not limited to a few that's willing to pay.
your average Joe doesn't have enough resources to test it out. That means at least 10,000 rounds or more are fired in a rapid session.
Above all else, if a bolt lasts until the gun needs to be fixed (like a rebarrel), at least that doesn't hurt the combat effectiveness, so most are still rolling with their mil-spec bolt.
Not sure where you are going with this but here are a couple of thoughts:
1) The Average Joe AR Owner doesn't fire over 1,000 rounds out of there rifle over it's lifetime;
2) Advertisers and industry shills are almost without exception trying to get the user to perceive a need for the greatest and latest - this is NOT limited to firearms by any means;
3) Some folks like to be part of the in-crowd by buying those items;
4) For 99.99% of users failure of any part on an AR, be it bolt, fire control unit, whatever is not a life or death situation - it means the end of a range trip, or dropping out of a match;
5) For the life or death users it seems to me that reasonable, PROVEN enhancements in design, plus regular inspection and replacement are the keys to reliability;
I was always concerned over extractor damage when we practiced fail to extract drills with our student officers. At one time I even suggested that we do a final armorer tear down and inspection, replacing the extractors are they had finished the firearms portion of the academy. When I considered the time involved and then the cost of three hundred whatever brand pistol extractors of the course of a year, I realized it wasn't a realistic solution.
More realistic would be an agency program which replaced every spring, the firing pin and the extractor, every three to five years.
Seems to me that is the reasonable and sensible way for the average weapon owner to go with defensive firearms.
Was this responsive to your post?
Not sure where you are going with this but here are a couple of thoughts:
1) The Average Joe AR Owner doesn't fire over 1,000 rounds out of there rifle over it's lifetime;
2) Advertisers and industry shills are almost without exception trying to get the user to perceive a need for the greatest and latest - this is NOT limited to firearms by any means;
3) Some folks like to be part of the in-crowd by buying those items;
4) For 99.99% of users failure of any part on an AR, be it bolt, fire control unit, whatever is not a life or death situation - it means the end of a range trip, or dropping out of a match;
5) For the life or death users it seems to me that reasonable, PROVEN enhancements in design, plus regular inspection and replacement are the keys to reliability;
I was always concerned over extractor damage when we practiced fail to extract drills with our student officers. At one time I even suggested that we do a final armorer tear down and inspection, replacing the extractors are they had finished the firearms portion of the academy. When I considered the time involved and then the cost of three hundred whatever brand pistol extractors of the course of a year, I realized it wasn't a realistic solution.
More realistic would be an agency program which replaced every spring, the firing pin and the extractor, every three to five years.
Seems to me that is the reasonable and sensible way for the average weapon owner to go with defensive firearms.
Was this responsive to your post?
Fair.
I’m looking for two things: a more cost effective solution and how do we test it out. Latter is probably the hardest.
I’d rather design a new gun that is slightly upsized than hope to capture market share from the glut of cheap AR bolts made.
constructor
07-25-23, 09:29
I’d rather design a new gun that is slightly upsized than hope to capture market share from the glut of cheap AR bolts made.
Someone should have done that 10 years ago- 2.5" long mag well and increased the barrel extension and bolt diameter .050"
constructor
07-25-23, 09:37
Fair.
I’m looking for two things: a more cost effective solution and how do we test it out. Latter is probably the hardest.
Like I said earlier it's easy I did it 13 years ago. A couple of CNCs at 100k each, need someone to figure out the machining process and write a program after the bolt is designed.
Just take the bolts to a lab for destructive testing.
One thing to keep in mind, there is a patent troll in Vegas that has a patent on any bolts larger than a standard AR15 bolt. He's just waiting for someone to infringe so he can sue. I'm the one that gave him the idea in 2007 and he tried to sue me in 2015 but, I had proof I was making the bolts before he filed for the patent.
Like I said earlier it's easy I did it 13 years ago. A couple of CNCs at 100k each, need someone to figure out the machining process and write a program after the bolt is designed.
Just take the bolts to a lab for destructive testing.
One thing to keep in mind, there is a patent troll in Vegas that has a patent on any bolts larger than a standard AR15 bolt. He's just waiting for someone to infringe so he can sue. I'm the one that gave him the idea in 2007 and he tried to sue me in 2015 but, I had proof I was making the bolts before he filed for the patent.
Wow, that's a lot of drama for a small improvement.
Apalogize I'm working earlier and don't have time to response. How's the compatibility with your new design?
You're also right on things were not made to last, that's not just firearms, it's mostly due to the fast-paced nature of modern technology and how most people want instant success. That's not how firearms work, where a small idea need year-over-year to polish.
I also think manufacturers are very short-sighted to let their own idea staying proprietary. This is the reason I look away from M4E1 and Knights. If they could release some of their design as a standard, it could very well be a win-win, but now you'll be forced to choose their own barrel and handguards. They're not bad, but not always fits one's need.
You know how fluidmaster makes the toilet flappers fail after being in the water so long so they can sell more flappers over and over?
This is the absolute essence of the American Mediocrity Syndrome that pollutes our production and design. Now I don't believe that the same country that blew up two space shuttles can build a decent automobile if their lives depended on it. But the Toiled flapper is a perfect example of the American culture of building garbage because most imbeciles will accept it. Shit! People still buy Chevy, Dodge and Ford garbage every day!
When it comes to ARs, there's certainly a large portion of buyers who just bee-bop into a gun store and are happy with some LWRC trash. Guy on this forum at least attempt to seek out the better/best option for the buck.
The people who had premature bolt failures may have just gotten a poorly heat treated batch. They also used their guns in an unusually harsh manner.
The average or even moderately abused civilian AR doesn’t even break the cheapest nitride bolt with any regularly that I’ve seen.
This is the absolute essence of the American Mediocrity Syndrome that pollutes our production and design. Now I don't believe that the same country that blew up two space shuttles can build a decent automobile if their lives depended on it. But the Toiled flapper is a perfect example of the American culture of building garbage because most imbeciles will accept it. Shit! People still buy Chevy, Dodge and Ford garbage every day!
When it comes to ARs, there's certainly a large portion of buyers who just bee-bop into a gun store and are happy with some LWRC trash. Guy on this forum at least attempt to seek out the better/best option for the buck.
I don't know, there's SpaceX. Do Europeans even launch rockets at this point?
But I see your point. Yes, good working men and women in this country are decreasing YoY. Still, last time I chat with my buddy in China, the birth rate expected to drop to 8M (that's a 1.45B country), so we'll see, I still have high hopes here.
The people who had premature bolt failures may have just gotten a poorly heat treated batch. They also used their guns in an unusually harsh manner.
The average or even moderately abused civilian AR doesn’t even break the cheapest nitride bolt with any regularly that I’ve seen.
That leads back to #1, where we don't exactly know how they're using their weapons. The most outrageous claim I've heard is from the Battlefield LV where he claims his SCAR survived 200K.
I've asked Lysander once, he thinks 100K is already an impossible goal for any bolt design.
I appreciate you resuming this conversation, though I get the sense it's been thought about quite a bit in the past. Maybe nowadays bolt breakage isn't as hot of an issue as before, with more reasonable gas port sizes, AGBs, trending toward longer gas systems, etc.
As an aside it would be cool if someone made an unpowered round counter that could be attached to the upper, like those mechanical step counters you can clip to your belt. An upper odometer, if you will. A recommended inspection and parts replacement schedule can be adjusted for the upper's configuration (i.e. 20" barrel vs overgassed 10.5”).
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constructor
07-25-23, 17:24
Wow, that's a lot of drama for a small improvement.
How's the compatibility with your new design?
That's the deal when all barrel extensions are the same the bolt has to work with them and that limits your design. It doesn't have to be exactly like the mil spec but it has to be close.
The other 3 designs I had used barrel extensions that matched the bolt but that only works for people who are having custom barrels made or can buy barrels without the extension installed and gas port drilled..
Back around 2010 9310 was the new alloy to use in bolts now that alloy has doubled in price. Any high strength alloy will be much more expensive than it was 10 years ago.
Easy button; carry spare MILSPEC Bolt, maybe even BCG.
I’m amazed at the “operators” showing up for Drills classes with Med gear, PEQs, etc.- but no spare bolt?
Maybe even a back up Carbine?
That's the deal when all barrel extensions are the same the bolt has to work with them and that limits your design. It doesn't have to be exactly like the mil spec but it has to be close.
The other 3 designs I had used barrel extensions that matched the bolt but that only works for people who are having custom barrels made or can buy barrels without the extension installed and gas port drilled..
Back around 2010 9310 was the new alloy to use in bolts now that alloy has doubled in price. Any high strength alloy will be much more expensive than it was 10 years ago.
Speaking of price, Are all the decent enhanced bolts cheaper in the past? They're all unobtainium now.
Back on topic. If price is no objective, is it possible to build a compatible but virtually unbreakable bolt, like what Carol Lewis has claimed?
If that's yes, then do you really have to modify the extension, just to get a cost-effective bolt design?
While we're at it, might be a perfect time to bring out what Chicom is doing:
https://youtu.be/bjsQ--XSviY
I wonder what's everyone's take on the BCG design. I'm skeptical, though.
to summarize:
1. a complete retaining pin mechanism vs. standard cotter pin.
2. fixed ejector.
3. extractor with dual oblique springs.
4. 4 lug design.
5. a lever to prevent cam pin from scratching the upper ("anti-pre-engagement").
Thrym makes a battery case for two CR 123s, I keep one with a Colt bolt with firing pin inserted, cam pin and retaining pin. It's a tidy lil pkg that stows easily. It will probably be easier to just grab the Glock if a bolt shits the bed.
constructor
07-25-23, 22:20
Speaking of price, Are all the decent enhanced bolts cheaper in the past? They're all unobtainium now.
Back on topic. If price is no objective, is it possible to build a compatible but virtually unbreakable bolt, like what Carol Lewis has claimed?
If that's yes, then do you really have to modify the extension, just to get a cost-effective bolt design?
You would need to look at the yield strength and charpy value of every possible alloy and all possible heat treats for those alloys to figure out which will give you the most strength without getting brittle.
One of the few companies that made enhanced bolts made the first few batches too hard, like many they thought the harder the stronger. The bolts chipped around the cam pin hole and corners of the lugs.
If you are only talking about 5.56 bolts then yes, you could make bolts that would last many thousand rounds without too much effort. We were a small shop but machined apx 300 bolts a week for almost 10 years and still have had none break or none reported.
Wasn't the premature bolt breakage issue identified shortly after the GWOT started as a heat treat issue?
Who is still experiencing short bolt life?
Something else of importance that is invaluable IMO is the amount data available on the actual mil-spec bolt/BCG since its inception. Everything from manufacturing processes, destructive testing, service life, failures, and millions being fielded across multiple wars.
Nothing else compares to the amount of data and lessons learned about the evolution of the M16, M4, AR platform and its components.
You would need to look at the yield strength and charpy value of every possible alloy and all possible heat treats for those alloys to figure out which will give you the most strength without getting brittle.
One of the few companies that made enhanced bolts made the first few batches too hard, like many they thought the harder the stronger. The bolts chipped around the cam pin hole and corners of the lugs.
If you are only talking about 5.56 bolts then yes, you could make bolts that would last many thousand rounds without too much effort. We were a small shop but machined apx 300 bolts a week for almost 10 years and still have had none break or none reported.
Yes, pushing a new standard for 5.56 barrel extension will be hard today, sometimes standards are best to start early. Pity that the industry in general are short-sighted and always keep design proprietary.
Also, why 7 locking lugs? Any historical reasons?
One more thing, I think people rarely talks about heat treatment when they're discussing bolt life, perhaps they didn't know better here?
Come to think about it, you can't separate design with the material you're using, and a good build quality can go a long way.
constructor
07-26-23, 15:09
Yes, pushing a new standard for 5.56 barrel extension will be hard today, sometimes standards are best to start early. Pity that the industry in general are short-sighted and always keep design proprietary.
Also, why 7 locking lugs? Any historical reasons?
The amount of rotation in the cam pin track is limited. If there were more lugs they would be smaller and weak, if less lugs there wouldn't be enough room on in the carrier to rotate the bolt enough.
The amount of rotation in the cam pin track is limited. If there were more lugs they would be smaller and weak, if less lugs there wouldn't be enough room on in the carrier to rotate the bolt enough.
I did thought about that before, which seven lugs, with all consideration, probably make the best balance between size and durability. Is it still relevant today, though? The Chinese 191 I've posted above uses four lugs, and the travel distance seems to be similar (unsure).
Of course, that's a different caliber to begin with, and the bolt life may not be that different due to multiple factors.
Large lugs don’t necessarily need to fully rotate / engage.
constructor
07-26-23, 18:03
You guys going to convince every barrel maker and extension manufacturer to change the design of the extension and make bolts that aren't compatible ? That will be an uphill battle.
I gather the OP is a China-born person who has moved here (?). Interesting to hear his take and suggestions/questions.
One thing Chinese that I would buy without hesitation are weapons (most of them at least). They can chrome-line the f**k out of a barrel and other parts. The AK, SKS, M1911A1, and even a few other guns are good-to-go. Actually even the M14 was okay; the receiver was forged and the barrels were chrome lined. The bolts and hammers had a rep for being "soft" and supposedly worsened an already long headspace. Nonetheless, those issues could be rectified.
The Stoner system has long had "upgrades", be it military or commercial. While the currently accepted mil-spec is 8620 for carriers and C158 for bolts (both phosphate finished) there are no doubt better options if you want to pony-up the $$$. While 9310 is newer I haven't read where it surpasses C158 as far as AR bolts go. I like some of the "wunder" finishes (as long as the bolt itself is mil-spec): Cryptic Coatings Mystic Black, LMT EBCG, even a well-done hard chrome job. Nitride I can take or leave. The LMT EBCG goes beyond just a finish.....it has slightly altered the function, but in a positive sense. It is also expensive as hell. I have a couple complete but I also have the Enhanced Bolt Carrier coupled with a Cryptic Coatings Mystic Black bolt.
You guys going to convince every barrel maker and extension manufacturer to change the design of the extension and make bolts that aren't compatible ? That will be an uphill battle.
Not really. Just wondering if 7-lug design is holding the system back, or if this question is relevant at all.
I gather the OP is a China-born person who has moved here (?). Interesting to hear his take and suggestions/questions.
One thing Chinese that I would buy without hesitation are weapons (most of them at least). They can chrome-line the f**k out of a barrel and other parts. The AK, SKS, M1911A1, and even a few other guns are good-to-go. Actually even the M14 was okay; the receiver was forged and the barrels were chrome lined. The bolts and hammers had a rep for being "soft" and supposedly worsened an already long headspace. Nonetheless, those issues could be rectified.
The Stoner system has long had "upgrades", be it military or commercial. While the currently accepted mil-spec is 8620 for carriers and C158 for bolts (both phosphate finished) there are no doubt better options if you want to pony-up the $$$. While 9310 is newer I haven't read where it surpasses C158 as far as AR bolts go. I like some of the "wunder" finishes (as long as the bolt itself is mil-spec): Cryptic Coatings Mystic Black, LMT EBCG, even a well-done hard chrome job. Nitride I can take or leave. The LMT EBCG goes beyond just a finish.....it has slightly altered the function, but in a positive sense. It is also expensive as hell. I have a couple complete but I also have the Enhanced Bolt Carrier coupled with a Cryptic Coatings Mystic Black bolt.
Sometimes these people make things really cheap and effective, then inevitably they got too proud of themselves, and quickly went downhill.
I read a book where it's written hundred years ago (https://www.amazon.com/Chinese-Characteristics-Arthur-H-Smith/dp/1910736880), where he describes their stuff being "both capable and useless". Accurate description most of the time.
A few things . . . .
1) The life of a bolt is governed by a) wear, or b) fatigue. With wear, the continual rubbing or loading of parts will eventually reduce the the size to where it will no longer function properly. This will probably take a lot of repetitions to ever become a factor, but it is possible to reduce the headspace dimensions to the point that it is excessive. As to fatigue;
There are two types of fatigue: high-cycle, and low cycle fatigue. High-cycle fatigue is the eventual cracking from repeated small stresses and is measured in the 10^6 cycles, for steel, there is a fatigue limit, a point that is the stress is kept below this point, the part can withstand infinite cycles. Low-cycle fatigue is when a part is repeatedly subject to stresses above the yield point, and is measured is 10^3 or less cycles, depending on how far above the yield stress it is subjected to. The M16 bolt design has areas around the locking lugs that are subjected to stresses above the yield point, and therefore always be subject to low-cycle fatigue.
https://i.imgur.com/PLqZUOX.png
Increasing the radius at the base of the lug will reduce the stresses, but I do not think it is possible to lower them to below the yield limit, let alone the fatigue limit. There is just not enough material.
Fatigue will be exacerbated by small discontinuities, such a corrosion pits, tool marks left over from the manufacturing processes, or micro-cracking inherent from hard chrome plating.
2) The 100,000 round limit I was quoted is based on a bolt made compatible with a standard M16 barrel extension. A completely different design, such as a tipping bolt of a FAL might be capable of such high usage without failure.
3) Lugs that do not full engage create bending moments, and possibly higher stresses. There is also the issue of compressive stress limits. In any case, the lugs size is limited by what will pass through the gaps in the extension.
4) There is a lot of information available free on the internet, it is just a matter of knowing where to look for it, or how to search for it.
5) Cost-vs-longevity. I can buy a regular AR bolt that will last 10,000 to 15,000 rounds for $50. Will I get more than 20,000 to 30,000 rounds out of a $100 bolt? If so, how much more? If it ain't more that 10% to 20% it ain't much of a bargain. The Government uses 25% as a cut-off, it the new part does not come it for 75% of the original design over a 5 year period, it is not worth the change. (Of course, that does include the non-recurring costs, such as engineering and testing cost, which can be substantial.) For me, 10,000 - 15,000 rounds is a lifetime, or two.
6) AISI 9310 is not a "new" alloy. It has been around since the 1940s, and was used in aircraft landing gear and for M60 bolts from the beginning. In fact, it was proposed as an alternate for AISI 8620 in M14 bolts. You may not have heard about it before 2010, but it has been around quite a while. AISI 9310 is also a very popular alloy of high demand gears.
7) The QZB 191 bolt rotates 45° vs the AR's 22.5°. One of the more interesting improvements if the method of getting longer extractor springs.
https://i.imgur.com/h4fGkHR.jpg
A few things . . . .
1) The life of a bolt is governed by a) wear, or b) fatigue. With wear, the continual rubbing or loading of parts will eventually reduce the the size to where it will no longer function properly. This will probably take a lot of repetitions to ever become a factor, but it is possible to reduce the headspace dimensions to the point that it is excessive. As to fatigue;
There are two types of fatigue: high-cycle, and low cycle fatigue. High-cycle fatigue is the eventual cracking from repeated small stresses and is measured in the 10^6 cycles, for steel, there is a fatigue limit, a point that is the stress is kept below this point, the part can withstand infinite cycles. Low-cycle fatigue is when a part is repeatedly subject to stresses above the yield point, and is measured is 10^3 or less cycles, depending on how far above the yield stress it is subjected to. The M16 bolt design has areas around the locking lugs that are subjected to stresses above the yield point, and therefore always be subject to low-cycle fatigue.
https://i.imgur.com/PLqZUOX.png
Increasing the radius at the base of the lug will reduce the stresses, but I do not think it is possible to lower them to below the yield limit, let alone the fatigue limit. There is just not enough material.
Fatigue will be exacerbated by small discontinuities, such a corrosion pits, tool marks left over from the manufacturing processes, or micro-cracking inherent from hard chrome plating.
2) The 100,000 round limit I was quoted is based on a bolt made compatible with a standard M16 barrel extension. A completely different design, such as a tipping bolt of a FAL might be capable of such high usage without failure.
3) Lugs that do not full engage create bending moments, and possibly higher stresses. There is also the issue of compressive stress limits. In any case, the lugs size is limited by what will pass through the gaps in the extension.
4) There is a lot of information available free on the internet, it is just a matter of knowing where to look for it, or how to search for it.
5) Cost-vs-longevity. I can buy a regular AR bolt that will last 10,000 to 15,000 rounds for $50. Will I get more than 20,000 to 30,000 rounds out of a $100 bolt? If so, how much more? If it ain't more that 10% to 20% it ain't much of a bargain. The Government uses 25% as a cut-off, it the new part does not come it for 75% of the original design over a 5 year period, it is not worth the change. (Of course, that does include the non-recurring costs, such as engineering and testing cost, which can be substantial.) For me, 10,000 - 15,000 rounds is a lifetime, or two.
6) AISI 9310 is not a "new" alloy. It has been around since the 1940s, and was used in aircraft landing gear and for M60 bolts from the beginning. In fact, it was proposed as an alternate for AISI 8620 in M14 bolts. You may not have heard about it before 2010, but it has been around quite a while. AISI 9310 is also a very popular alloy of high demand gears.
7) The QZB 191 bolt rotates 45° vs the AR's 22.5°. One of the more interesting improvements if the method of getting longer extractor springs.
https://i.imgur.com/h4fGkHR.jpg
I shall read it multiple times to make sure I fully understand.
In the meantime...
There are two ways to look at this problem: #1, whatever we have now is not long enough for most situations, which isn't the case, or #2, it’s much shorter than every other design out there, which I don’t know if that’s the case.
You've mentioned FAL and I'll bet that's probably one of the longest-lasting designs available. Most other designs (99% maybe?) will break within this time period, so... The most reasonable goal is to make a bolt that's on par, or better than most others. Given that most other rifles are heavily inspired by the AR-15 and the 18, This might not be a tough goal. Just costly for individuals.
Or not?
Based on the reply on the cam pin thread where you’ve mentioned that .mil never went above and beyond 36K for testing, that means they’re looking for something that’s 2.4x-3.6x better at a cost of $120-180. Is this why the M4 PIP dropped? Mainly because nobody can meet the price range, or they can’t meet the 2.4-3.6x goal?
200K is what I've heard from Battlefield LV where he claimed his SCAR has reached. Sounds fishy but oh well, no evidence against it either.
Also, any (theoretical) pros and cons on the extractor design of the 191? Maybe it's just for a longer spring? I don't know if these springs being oblique improves reliability.
Who is having bolt life issues?
Also, any (theoretical) pros and cons on the extractor design of the 191? Maybe it's just for a longer spring? I don't know if these springs being oblique improves reliability.
Longer springs usually mean less stress in the spring.
Longer springs usually mean less stress in the spring.
There’s that. Though have two long holes beside the firing pin hole in the center, sounds like a trade-off.
Back to the AR, last time I checked the LMT bolt costs $389.00. If we want 1:1 on cost and performance gains, that’s 7.78x more expensive and it should deliver between 77.8K and 116.7K.
If you said even the FAL might not make it that far…yeah probably not 1:1 here.
Based on the reply on the cam pin thread where you’ve mentioned that .mil never went above and beyond 36K for testing, that means they’re looking for something that’s 2.4x-3.6x better at a cost of $120-180. Is this why the M4 PIP dropped? Mainly because nobody can meet the price range, or they can’t meet the 2.4-3.6x goal?
Well, after those 36,000 rounds most of those rifles went through 2 or three bolts, so 12 to 15 K rounds is the current life, with a current price of about $45 each.
So, the projected total cost of all the bolts you buy after five years, plus the non-recurring cost has to be 25% less that the projected cost of all the current design bolts you would have bought over those five years.
If you burn through 10,000 bolts per year, at $50 each, the five year cost is $50,000. The cost of a drawing change is about $50,000, so any change is pretty much a non-starter. If you go through 100,000 bolts per year, you spend $500,000, and for it to be worth it you would have to reduce the yearly consumption to 7,250 bolts So, you see the life improvement percent is based on the number of bolts consumed each year, which in turn is based on the number of rifles overhauled per year and the percent of those that require new bolts.
The M4 PIP was to update all existing M4s and M4A1s to the latest M4A1 standard (full, automatic fire, heavy barrel, ambidextrous selector), and as far as I know, was completed. Or, at least converted enough weapons to cover current issue requirements.
Failure2Stop
07-31-23, 11:20
If you want better bolt life than a common AR-15 bolt, the first step is to design a new bolt and barrel extension.
Well, after those 36,000 rounds most of those rifles went through 2 or three bolts, so 12 to 15 K rounds is the current life, with a current price of about $45 each.
So, the projected total cost of all the bolts you buy after five years, plus the non-recurring cost has to be 25% less that the projected cost of all the current design bolts you would have bought over those five years.
If you burn through 10,000 bolts per year, at $50 each, the five year cost is $50,000. The cost of a drawing change is about $50,000, so any change is pretty much a non-starter. If you go through 100,000 bolts per year, you spend $500,000, and for it to be worth it you would have to reduce the yearly consumption to 7,250 bolts So, you see the life improvement percent is based on the number of bolts consumed each year, which in turn is based on the number of rifles overhauled per year and the percent of those that require new bolts.
The M4 PIP was to update all existing M4s and M4A1s to the latest M4A1 standard (full, automatic fire, heavy barrel, ambidextrous selector), and as far as I know, was completed. Or, at least converted enough weapons to cover current issue requirements.
So it’s 12-15k a result of typical combat use, or a harsh firing schedule?
If you want better bolt life than a common AR-15 bolt, the first step is to design a new bolt and barrel extension.
Seems like something a high quality AR manufacturer would do over a decade ago.
It seems so obvious in hindsight...
If you want better bolt life than a common AR-15 bolt, the first step is to design a new bolt and barrel extension.
If you want better bolt life than a common AR-15 bolt, the first step is to design a new bolt and barrel extension.
and then open source it so the industry can standardize
Can the round being used cycle a radial BCG?
So it’s 12-15k a result of typical combat use, or a harsh firing schedule?
The usual 120 round test cycle.
One magazine semi-auto at 10 -12 rpm
One magazine full auto at 120 - 150 rpm
One magazine semi-auto at 10 -12 rpm
One magazine full auto at 120 - 150 rpm
Cool to ambient. Repeat until 600 rounds fired.
Wipe down and re-lubricate every 600 rounds.
Fully disassemble, clean and inspect every 1,200 rounds.
Accuracy is checked with the first semi-auto ten rounds in a 1,200 cycle, If the cyclic rate is measure, it is done with a mag-dump of the first full auto magazine in a 1,200 cycle.
turnburglar
08-05-23, 19:08
Here are some incredibly anecdotal observations of my own....
Awhile back I remember reading that some shooters speculated that higher pressure ammo would put increased stress on the 'fragile' AR15 bolt. I inadvertently tested this hypothesis over the last couple years of reloading and competitive shooting. I have one 9310 bolt that easily has 4-5k of some VERY spicy reloads on it, and the lugs dont look any worse than would be expected of a bolt with a similar round count of PMC. How spicy am I talking about? Hogdon website calls H335 max at 22.7gr (55k psi) for a 77gr SMK. I was using 24.3 gr for a long time, and only backed it down for shooting in the summer because I became tired of pulling primers out of the receiver. I would even speculate this bolt could shoot another 5k of these 556 pressure reloads without giving up a lug.
This system is not as delicate as some people make it sound.
I have one 9310 bolt that easily has 4-5k of some VERY spicy reloads on it,
Brand?
turnburglar
08-06-23, 13:12
Brand?
IIRC 'White Label Armory'?
My buddy is a dealer and I bought x4 off of him when he got a ton in for sub $100. I thought it would be cool to see how long some no name bolt lasts, and I wanted some spare BCG's.
Failure2Stop
08-08-23, 08:23
Here are some incredibly anecdotal observations of my own....
Awhile back I remember reading that some shooters speculated that higher pressure ammo would put increased stress on the 'fragile' AR15 bolt. I inadvertently tested this hypothesis over the last couple years of reloading and competitive shooting. I have one 9310 bolt that easily has 4-5k of some VERY spicy reloads on it, and the lugs dont look any worse than would be expected of a bolt with a similar round count of PMC. How spicy am I talking about? Hogdon website calls H335 max at 22.7gr (55k psi) for a 77gr SMK. I was using 24.3 gr for a long time, and only backed it down for shooting in the summer because I became tired of pulling primers out of the receiver. I would even speculate this bolt could shoot another 5k of these 556 pressure reloads without giving up a lug.
This system is not as delicate as some people make it sound.
Crack propagation, fatigue wear, and yield force are not things that can be seen by the human eye or predicted without task-specific software and properly used force sensors.
That doesn't mean that it *won't* do another 5k, but speculation on the matter would require a lot more data.
Carpenter 158 = good
AISI 9310 = bad
But, is that really the case?
What is the difference between 158 and 9310? 9310 has one kilogram (2.2 pounds) of molybdenum per ton of steel, 158 doesn't have any, all the other important alloying elements of 9310 can fall within 158's tolerances.
So what does molybdenum bring to the alloy? Molybdenum lowers the required quench rate. When steel is heated and quenched the quench rate, or the speed at which the steel must be cooled in order the maintain the desired crystalline structure, must be fast. However, when the rate is very fast the process can become unstable and you get variations in the crystal structure formed. Molybdenum and manganese allow for slower, more controlled cooling. It also improves the corrosion resistance, toughness and tensile strength.
There really isn't any difference between the two.
Why was Carpenter 158 chosen and not 9310? Well, I wasn't there when the decision was made but I have had similar experiences of trying to chose and alloy. Normally, if you are a smallish company, you don't have an expert metallurgist on staff, but you know who does? That's right a steel mill. So you call up a well known and respected mill and give their expert your requirements for the steel and ask him/her what the best alloy would be, and they will be happy to tell you which of their products suits your needs. Now, if they manufacture a proprietary alloy that is only available from them, but is almost exactly the same as a standardized specification alloy that you can get anywhere, which do you think will be the suggestion?
Why is Carpenter 158 still the MIL-SPEC? Because the Government does not own the drawings and would have to ask Colt to change the drawing and have a metallurgist write-up a report explaining why the change would not alter the end product. This would cost money. And, since there is not a shortage of Carpenter 158, and the price is not outrageous, it would be wasteful change something that does not need to be changed. If the alloy were some foreign standard alloy that is not normally supplied in the US, then such a change might be justified. And this is exactly what happened with the M240 and M249. The bolts for the M249 was spec'ed out as ISO grade, and that was changed to a standard AISI grade for US production, 9310 as a matter of fact.
The usual 120 round test cycle.
One magazine semi-auto at 10 -12 rpm
One magazine full auto at 120 - 150 rpm
One magazine semi-auto at 10 -12 rpm
One magazine full auto at 120 - 150 rpm
Cool to ambient. Repeat until 600 rounds fired.
Wipe down and re-lubricate every 600 rounds.
Fully disassemble, clean and inspect every 1,200 rounds.
Accuracy is checked with the first semi-auto ten rounds in a 1,200 cycle, If the cyclic rate is measure, it is done with a mag-dump of the first full auto magazine in a 1,200 cycle.
10-12 and 120-150? That seems slow.
Another (relatively good) theoretical question just poped in my head: If AR bolt simply don't have enough material, then, how much do we need to eliminate these weak spots? I wonder how's other platform with AR-pattern bolts are doing? Maybe not the exact number, but can they be 2x-3x or even more better?
and then open source it so the industry can standardize
If the aforementioned one-piece-of-steel FAL is close to 100K, and everyone else varies between... Will that make a huge difference?
The other thing people seemingly forget is numbers are meaningless without context. That's probably what magical "3x improvement!" is.
10-12 and 120-150? That seems slow.
Another (relatively good) theoretical question just poped in my head: If AR bolt simply don't have enough material, then, how much do we need to eliminate these weak spots? I wonder how's other platform with AR-pattern bolts are doing? Maybe not the exact number, but can they be 2x-3x or even more better?
10 to 12 rpm = one round every 5 to 6 seconds, which is the maximum sustained rate of fire.
120 to 150 rpm is a 3 to 5 round burst every three to four seconds.
It's enough to get the barrel up to about 500 to 600 degrees F after 120 rounds.
The weak spot in the bolt is the gap for the extractor. The two lugs flanking the extractor are twisted into the gap on loading.
https://i.imgur.com/6M0weUR.png
https://i.imgur.com/PLqZUOX.png
The easiest way to improve the strength of the design would be the increase the width of the base of the lug, giving a trapezoidal shape when viewed from the front, which is what was done to the AR-10 bolt after AI took over the design from Armalite. But, that requires a modification to the barrel extension, so you are stuck with trying to figure out how to increase the radii around the bolt lug without running afoul of the extension.
Oh, and by the way, going back to 9310, it is the Mil-spec material for the M27 IAR bolt, which is dimensionally the same as the AR-15 bolt in the locking lug area.
constructor
08-17-23, 09:25
First 2 are 5.56, 6.8 Super bolts designed to work with mil spec barrel extensions., Titan bolt-6mm ARC/7.62x39, 750XD for 6BRX & 270MSR, 800 series -that bolt is for the 6.8 but the 800 series was originally designed for the 6BRX(.473" dia base) all were machined from 9310 Vac Arc. We machined them for apx 10 years and the only reported broken bolt was a 6.8 that was subjected to an overcharge, guy left pistol powder in his powder measure then dumped a normal rifle powder on top. It blew the upper apart but did not damage the barrel.
70684
10 to 12 rpm = one round every 5 to 6 seconds, which is the maximum sustained rate of fire.
120 to 150 rpm is a 3 to 5 round burst every three to four seconds.
It's enough to get the barrel up to about 500 to 600 degrees F after 120 rounds.
The weak spot in the bolt is the gap for the extractor. The two lugs flanking the extractor are twisted into the gap on loading.
https://i.imgur.com/PlWF7j3.jpg
https://i.imgur.com/PLqZUOX.png
The easiest way to improve the strength of the design would be the increase the width of the base of the lug, giving a trapezoidal shape when viewed from the front, which is what was done to the AR-10 bolt after AI took over the design from Armalite. But, that requires a modification to the barrel extension, so you are stuck with trying to figure out how to increase the radii around the bolt lug without running afoul of the extension.
Oh, and by the way, going back to 9310, it is the Mil-spec material for the M27 IAR bolt, which is dimensionally the same as the AR-15 bolt in the locking lug area.
Thanks for telling me that German bolts aren't made out of unobtainium...
Does that mean these lugs failed like a domino effect? With these two lugs break first, it'll adds up more load on others, forcing them to break prematurely, one by one. If you can improve these two lugs, it'll stop (or delay) this phenomenon.
First 2 are 5.56, 6.8 Super bolts designed to work with mil spec barrel extensions., Titan bolt-6mm ARC/7.62x39, 750XD for 6BRX & 270MSR, 800 series -that bolt is for the 6.8 but the 800 series was originally designed for the 6BRX(.473" dia base) all were machined from 9310 Vac Arc. We machined them for apx 10 years and the only reported broken bolt was a 6.8 that was subjected to an overcharge, guy left pistol powder in his powder measure then dumped a normal rifle powder on top. It blew the upper apart but did not damage the barrel.
70684
Nice. What's the longest record (round count) you've had on your 5.56, and how much better on the other big calibers?
constructor
08-17-23, 09:49
Lugs are .277" long with a recess of .124" deep so you have full strength attachment/support of .153". The web/rim is missing on one side of the lugs at the extractor is why those lugs break first.
The lugs are .100" wide, every .001" the width is increased increases strength 1%. Larger radii at the base of the lugs increase strength. Longer lugs would increase strength.
If you deepen the recess like they did with the Grendel, it will decrease strength of the bolt lugs.
constructor
08-17-23, 10:23
Nice. What's the longest record (round count) you've had on your 5.56, and how much better on the other big calibers?
No idea what personal round count is on any bolt. When I made the first batch I sent then out to a lab for destructive testing. One test was maximum thrust which showed the Superbolts to be 17-18% stronger than mil spec bolts made of C158, I used Microbest and Colt bolts to test against. The other was repetitive 10,000 cycles at the same value that a 5.56 creates somewhere around 6500-7000lbs/sqin IIRC.
The only 5.56 bolts I've ever broken were Y/M in the late 90s and they broke at the cam pin hole so I increased the diameter of the bolt at the cam pin hole, I believe JP Enterprises has started doing the same to their bolts over the last 5 year or so.
I designed the 800 series bolts so I could build a AR15 chambered in 6BRX, 95SMK at 3200fps, 22" barrel. The first one I made in 2007 and still hasn't broke but they don't get the round count that a 5.56 does.
ETA- As I've said before, there are many ways to increase the strength/durability of an AR15 bolt it just depends on if it must be made to work within the mil spec barrel extension limitations or will it be proprietary. Decrease the length of the shank on the barrel .015", leave the extension alone and increase the length of the lugs .015", that will increase the strength of the bolt 10%.
Leave the barrel shank at the same length, increase the barrel extension length .015" along with the lugs and gain 10%. Combine the lug length change with a different lug shape with more attachment area and it may be possible to get 25-30%.
Back around 2010 there were several companies that claimed they had made bolts twice as strong, that was just outlandish claims. There are just too many limitations to see that kind of increase.
Lugs are .277" long with a recess of .124" deep so you have full strength attachment/support of .153". The web/rim is missing on one side of the lugs at the extractor is why those lugs break first.
The lugs are .100" wide, every .001" the width is increased increases strength 1%. Larger radii at the base of the lugs increase strength. Longer lugs would increase strength.
That would be true if the lugs were only loaded in shear. Unfortunately, there is a considerable bending moment due to the lugs trying to fold over into the extractor gap. Making the lugs longer would not help with the bending moment, and might exacerbate it. Also due to the bending moments the increase in strength is not linear.
Increasing the radii R1 and R2 help a little in reducing stress concentrations, but bigger gains are seen with the last three bolts show in the image. The primary reason these are so much stronger is the increase in width at the base of the lugs. The added strength is not due to the increase in shear area, but the added stability to resist bending.
https://i.imgur.com/DAGAVg2.png
If you could keep the top of the lugs the same width (0.102") but kick the sides out to a 15 degree included angle, you could increase the lug base by 30% and stabilize the lug much better. In fact, if you look at a Stoner 63 bolt, the bolt lugs were made wider.
No idea what personal round count is on any bolt. When I made the first batch I sent then out to a lab for destructive testing. One test was maximum thrust which showed the Superbolts to be 17-18% stronger than mil spec bolts made of C158, I used Microbest and Colt bolts to test against. The other was repetitive 10,000 cycles at the same value that a 5.56 creates somewhere around 6500-7000lbs/sqin IIRC.
The only 5.56 bolts I've ever broken were Y/M in the late 90s and they broke at the cam pin hole so I increased the diameter of the bolt at the cam pin hole, I believe JP Enterprises has started doing the same to their bolts over the last 5 year or so.
I designed the 800 series bolts so I could build a AR15 chambered in 6BRX, 95SMK at 3200fps, 22" barrel. The first one I made in 2007 and still hasn't broke but they don't get the round count that a 5.56 does.
ETA- As I've said before, there are many ways to increase the strength/durability of an AR15 bolt it just depends on if it must be made to work within the mil spec barrel extension limitations or will it be proprietary. Decrease the length of the shank on the barrel .015", leave the extension alone and increase the length of the lugs .015", that will increase the strength of the bolt 10%.
Leave the barrel shank at the same length, increase the barrel extension length .015" along with the lugs and gain 10%. Combine the lug length change with a different lug shape with more attachment area and it may be possible to get 25-30%.
Back around 2010 there were several companies that claimed they had made bolts twice as strong, that was just outlandish claims. There are just too many limitations to see that kind of increase.
As to people marketing bolts and making claims to 10% or more increases in life, unless they get very specific on how they do it, I would be wary. Back in 2014, the Army asked for submissions from industry to increase the the bolt life by a minimum of 10%. Nobody met the target.
However, one thing that did come out of this effort was it was demonstrated that with just low plasticity burnishing (LPB) of the radius behind the locking lugs you can get almost 100% increase in bolt life. So, you can get considerable gains within the existing envelope, if you spend the money in the right place. I do not think anybody is currently offering this type of bolt though. It is probably expensive to impliment on a industrial scale.
constructor
08-17-23, 15:47
That would be true if the lugs were only loaded in shear. Unfortunately, there is a considerable bending moment due to the lugs trying to fold over into the extractor gap. Making the lugs longer would not help with the bending moment, and might exacerbate it. Also due to the bending moments the increase in strength is not linear.
Increasing the radii R1 and R2 help a little in reducing stress concentrations, but bigger gains are seen with the last three bolts show in the image. The primary reason these are so much stronger is the increase in width at the base of the lugs. The added strength is not due to the increase in shear area, but the added stability to resist bending.
https://i.imgur.com/DAGAVg2.png
If you could keep the top of the lugs the same width (0.102") but kick the sides out to a 15 degree included angle, you could increase the lug base by 30% and stabilize the lug much better. In fact, if you look at a Stoner 63 bolt, the bolt lugs were made wider.
The lugs would be longer to the rear not the front making more full strength attachment. The recess would be the same .124"
constructor
08-17-23, 15:56
10 to 12 rpm = one round every 5 to 6 seconds, which is the maximum sustained rate of fire.
120 to 150 rpm is a 3 to 5 round burst every three to four seconds.
It's enough to get the barrel up to about 500 to 600 degrees F after 120 rounds.
The weak spot in the bolt is the gap for the extractor. The two lugs flanking the extractor are twisted into the gap on loading.
https://i.imgur.com/6M0weUR.png
.
What does this drawing represent? A cutaway through which direction?
As to people marketing bolts and making claims to 10% or more increases in life, unless they get very specific on how they do it, I would be wary. Back in 2014, the Army asked for submissions from industry to increase the the bolt life by a minimum of 10%. Nobody met the target.
However, one thing that did come out of this effort was it was demonstrated that with just low plasticity burnishing (LPB) of the radius behind the locking lugs you can get almost 100% increase in bolt life. So, you can get considerable gains within the existing envelope, if you spend the money in the right place. I do not think anybody is currently offering this type of bolt though. It is probably expensive to impliment on a industrial scale.
Does that also includes LMT's enhanced bolt?
Is "stronger" and "longer" the same here?
As to people marketing bolts and making claims to 10% or more increases in life, unless they get very specific on how they do it, I would be wary. Back in 2014, the Army asked for submissions from industry to increase the the bolt life by a minimum of 10%. Nobody met the target.
However, one thing that did come out of this effort was it was demonstrated that with just low plasticity burnishing (LPB) of the radius behind the locking lugs you can get almost 100% increase in bolt life. So, you can get considerable gains within the existing envelope, if you spend the money in the right place. I do not think anybody is currently offering this type of bolt though. It is probably expensive to impliment on a industrial scale.
LMT standard bolts have an annular radius behind the lugs. Does this accomplish the same as LPB?
and then open source it so the industry can standardize
Yes..
What does this drawing represent? A cutaway through which direction?
The drawing on the left shows the bending of the lugs from the front view. They want to collapse into the extractor slot.
The drawing on the right is a view from above the lugs.
Perhaps a better picture than the left would be this:
https://i.imgur.com/lcpE1GS.jpg
LMT standard bolts have an annular radius behind the lugs. Does this accomplish the same as LPB?
No, what they are doing is just increasing the radius and reducing the stress concentration at the discontinuity. There are several ways to do that, which one you choose depends on the length of the flat area you need on the back of the lug to properly mate with the extension lug and not have the extension encroach into the radius and how much of a radius increase you desire.
https://i.imgur.com/q3vHLJl.jpg
(side view of lug)
Low plasticity burnishing is introducing a compressive stress on the surface of the material, same as shot peening, but in a more controlled manner. It is accomplished by rolling a a tool over a high stress area under pressure.
https://i.imgur.com/7yJemxj.jpg
LMT standard bolts have an annular radius behind the lugs. Does this accomplish the same as LPB?
No, what they are doing is just increasing the radius and reducing the stress concentration at the discontinuity. There are several ways to do that, which one you choose depends on the length of the flat area you need on the back of the lug to properly mate with the extension lug and not have the extension encroach into the radius and how much of a radius increase you desire.
https://i.imgur.com/q3vHLJl.jpg
(side view of lug)
Low plasticity burnishing is introducing a compressive stress on the surface of the material, same as shot peening, but in a more controlled manner. It is accomplished by rolling a a tool over a high stress area under pressure.
https://i.imgur.com/7yJemxj.jpg
Another thing to add, they're using proprietary alloy to begin with. Contrary to popular belief, I doubt it's the "Aermet 100".
If they aren't one of those who failed to meet the 10% increase, then I doubt that's something cheap enough to equip the entire army at a reasonable cost. Same for Knights, too.
Does that also includes LMT's enhanced bolt?
Is "stronger" and "longer" the same here?
No, because shear is not the primary failure mode, bending is. And, making the lugs longer does not decrease the bending moments, in fact, depending on what is getting longer, it might exacerbate the problem.
The shear load can easily be calculated, it is just the bolt thrust (pressure times rim diameter, or about 7,000 pounds) divided by the shear area, or the foot print of the lug on the bolt (0.102" x 0.278" = 0.028356 sq in)
Doing the math you find the shear stress is 36,265 psi. Hardened 1080 steel can hold that even with a safety factor of 1.5. For heat treated 158 or 9310 the shear strength is in the neighborhood of 80,000 psi
If you go back to the stress model of the bolt shown in post #50, the red areas of the bolt are seeing a tensile stress of around 155,000 psi.
EDIT: The yield strength of 158 and 9310 heat treated in the normal manner is around 135,000 - 140,000 psi.
No, because shear is not the primary failure mode, bending is. And, making the lugs longer does not decrease the bending moments, in fact, depending on what is getting longer, it might exacerbate the problem.
The shear load can easily be calculated, it is just the bolt thrust (pressure times rim diameter, or about 7,000 pounds) divided by the shear area, or the foot print of the lug on the bolt (0.102" x 0.278" = 0.028356 sq in)
Doing the math you find the shear stress is 36,265 psi. Hardened 1080 steel can hold that even with a safety factor of 1.5. For heat treated 158 or 9310 the shear strength is in the neighborhood of 80,000 psi
If you go back to the stress model of the bolt shown in post #50, the red areas of the bolt are seeing a tensile stress of around 155,000 psi.
EDIT: The yield strength of 158 and 9310 heat treated in the normal manner is around 135,000 - 140,000 psi.
Okay, going back to #50, the "big" red spot under these lugs on the edge is mainly due to bending. Am I getting it this time?
constructor
08-17-23, 23:14
The drawing on the right is a view from above the lugs.
Load coming from where?
Load coming from where?
See if I can explain in the simplest term possible:
he's talking about two lugs close to the extractor, because they're close to that big hole (extractor cutout), they want to collapse into each other.
When they do that, they stress the material surrounds them. With these "wall lugs" chiped off, if you will, it adds more loads to the rest of the five, and they'll fail by the weakest one. AR bolt lugs always break in a sequence.
70688
Thus, in order to extend your bolt life, the #1 issue is making these walls stronger. If you can do that, not only you're preventing the break point, but you're also not overloading rest of these lugs.
The advantage of these huge radius designs weren't just about reduce stress, but with more material, you're connecting them like a solid one-piece and making them much stronger. That won't go well with the current established norm, and people who discover this simple trick always tend to milk quick profits than make it a standard, thus you're forced to over-engineer the old design. Good news is, as long you're not selling snake-oils, it's still possible to do, albeit very tricky and expensive.
constructor
08-18-23, 09:30
See if I can explain in the simplest term possible:
he's talking about two lugs close to the extractor, because they're close to that big hole (extractor cutout), they want to collapse into each other.
When they do that, they stress the material surrounds them. With these "wall lugs" chiped off, if you will, it adds more loads to the rest of the five, and they'll fail by the weakest one. AR bolt lugs always break in a sequence.
70688
Thus, in order to extend your bolt life, the #1 issue is making these walls stronger. If you can do that, not only you're preventing the break point, but you're also not overloading rest of these lugs.
The advantage of these huge radius designs weren't just about reduce stress, but with more material, you're connecting them like a solid one-piece and making them much stronger. That won't go well with the current established norm, and people who discover this simple trick always tend to milk quick profits than make it a standard, thus you're forced to over-engineer the old design. Good news is, as long you're not selling snake-oils, it's still possible to do, albeit very tricky and expensive.
Yes , I understand why the 2 lugs fail first and partially why I designed the 800 series like I did. With most machine shops we have CNC lathes and CNC mills that will do certain things easier/quicker than others so we must take that into consideration when designing parts. Most all ar15 bolt lugs are broach cut, but for me to make several different lug designs it was better for me to design them where I could change the shape by simply rewriting a few lines in the program and I could cut both the bolt lugs and barrel extension on the same machine with a mirror program.
The strongest bolt lug design would be a triangle that fully supports/add strength to the rim around the recess but that shape would result in a diamond shaped contact patch between the bolt lugs and extension lugs and the size of the contact patch would not support the thrust. The next best is the shape I used and it's easier to cut on a mill with simple end mills.
It seems you are looking for compatibility with standard barrel extensions and possibly even completed barrels so you can just use bolts on existing pieces. If that is the case then you are stuck with very few options. You can increase the radii at the base of the lugs a small amount like I did with the superbolt, increase the diameter of the rim around the recess like I did and find a stronger alloy that is tough but not brittle with a good charpy value and then give it the best heat treat you can.
You started the post, what is your objective? I mean are you going to produce bolts like have some company machine them for you or are you going to start a shop and machine them in house or is this just a discussion talking about how someone else should do it?
For 99.999% of the people out there it would be easier to just go buy a Knights rifle with the E3 bolt and call it a day or continue on like everyone has been doing for 30 years and replace the cheap bolts at 5000rnd intervals.
But then again for the shop owner like me I just had 3 machines running those same parts over and over every day and each machine making $4 a minute or 3 machines making $720/hr for 8-9 years it's a good money maker even if I didn't have other machines making other parts.
Yes , I understand why the 2 lugs fail first and partially why I designed the 800 series like I did.
You started the post, what is your objective?
Well, at first I thought you can easily double or triples the life and AR bolts will typically lasts 20k. Turns out these aren't the case.
For now, in order to double the 10k-15k life, how much work can be done based on the current extension, and what's the cost?
Yes , I understand why the 2 lugs fail first and partially why I designed the 800 series like I did. With most machine shops we have CNC lathes and CNC mills that will do certain things easier/quicker than others so we must take that into consideration when designing parts. Most all ar15 bolt lugs are broach cut, but for me to make several different lug designs it was better for me to design them where I could change the shape by simply rewriting a few lines in the program and I could cut both the bolt lugs and barrel extension on the same machine with a mirror program.
The strongest bolt lug design would be a triangle that fully supports/add strength to the rim around the recess but that shape would result in a diamond shaped contact patch between the bolt lugs and extension lugs and the size of the contact patch would not support the thrust. The next best is the shape I used and it's easier to cut on a mill with simple end mills.
It seems you are looking for compatibility with standard barrel extensions and possibly even completed barrels so you can just use bolts on existing pieces. If that is the case then you are stuck with very few options. You can increase the radii at the base of the lugs a small amount like I did with the superbolt, increase the diameter of the rim around the recess like I did and find a stronger alloy that is tough but not brittle with a good charpy value and then give it the best heat treat you can.
You started the post, what is your objective? I mean are you going to produce bolts like have some company machine them for you or are you going to start a shop and machine them in house or is this just a discussion talking about how someone else should do it?
For 99.999% of the people out there it would be easier to just go buy a Knights rifle with the E3 bolt and call it a day or continue on like everyone has been doing for 30 years and replace the cheap bolts at 5000rnd intervals.
But then again for the shop owner like me I just had 3 machines running those same parts over and over every day and each machine making $4 a minute or 3 machines making $720/hr for 8-9 years it's a good money maker even if I didn't have other machines making other parts.
That's what I don't get now. At first glance, it seems like the old extension is obsolete, then you keep hearing promising techniques. LPB being one, then LMT on the other hand stuck with their enhanced bolt even with their proprietary barrel extension, people tend to view the E-bolt is on-par with Knights. You'd think they'll make something similar to Knights with their MRP, but they didn't.
Well is the old extension really that bad then?
I also think there are plenty other designs that utilize a square, 7-lug design, yet people claimed they could easily lasts 2x or more, AUG being one example, it's ever-so-slightly larger.
When I'm trying to search th topic, I keep getting bits and pieces all over the net, it can took me hours to search and I'll have to figure out how which is what I need, and put them altogether. I'm sure I made mistakes down the road.
ViniVidivici
08-18-23, 10:35
Well, at first I thought you can easily double or triples the life and AR bolts will typically lasts 20k. Turns out these aren't the case.
For now, in order to double the 10k-15k life, how much work can be done based on the current extension, and what's the cost?
So, what's your objective here?
constructor
08-18-23, 10:38
Well, at first I thought you can easily double or triples the life and AR bolts will typically lasts 20k. Turns out these aren't the case.
For now, in order to double the 10k-15k life, how much work can be done based on the current extension, and what's the cost?
One problem now is steel cost. I don't know about all the other alloy cost but 9310 Vac Arc has doubled in price from 2009 until last year when I wanted to run some test pieces.
I called my normal supplier to get 2 -12' sticks when I normally purchased a semi load. He sent the order to a smaller house who quoted me around $1250/ 12' stick. That equates to apx $28/bolt.
Carbide end mill prices have tripled. The companies like LMT and LWRC who are charging $150/bolt are probably spot on now, I was selling them for less than $100 from 2009-2017.
For someone like me having a bolt that could fail anywhere from 5000 to 20000 rounds and not knowing when is not a good option, I replace my barrels more often than 5000 so I toss both the barrel and bolt and start with new parts at the same time and never worry about either failing. I mean to get to 5000 I just spent $3700+- on ammo what's $250 for a barrel and $70 for a bolt?
As for military armorers, they are using our tax money so why wouldn't they continue on doing what they do and replace at safe intervals.
constructor
08-18-23, 10:45
That's what I don't get now. At first glance, it seems like the old extension is obsolete, then you keep hearing promising techniques. LPB being one, then LMT on the other hand stuck with their enhanced bolt even with their proprietary barrel extension, people tend to view the E-bolt is on-par with Knights. You'd think they'll make something similar to Knights with their MRP, but they didn't.
Well is the old extension really that bad then?
I also think there are plenty other designs that utilize a square, 7-lug design, yet people claimed they could easily lasts 2x or more, AUG being one example, it's ever-so-slightly larger.
When I'm trying to search th topic, I keep getting bits and pieces all over the net, it can took me hours to search and I'll have to figure out how which is what I need, and put them altogether. I'm sure I made mistakes down the road.
Several years ago Cris Murray(AMU) contacted me about making some test bolts to convert a MG42 to his new 7mmUIAC caliber. His design which I am sure is the normal MG42 design had 5 big lugs. After making them and holding them up to an AR15 bolt they were massive. IF anyone/everyone was agreeable to changing the barrel extension the sky is the limit.
Several years ago Cris Murray(AMU) contacted me about making some test bolts to convert a MG42 to his new 7mmUIAC caliber. His design which I am sure is the normal MG42 design had 5 big lugs. After making them and holding them up to an AR15 bolt they were massive. IF anyone/everyone was agreeable to changing the barrel extension the sky is the limit.
It's an uphill battle that most don't want to fight in the first place. I wish someone can redesign the extension and open source his work.
I also don't know how much potential there is under the current design, especially comparing to others. IF (big if) LMT's work can easily match Knights and other service rifles (AUG, G36/SCAR...), then it's not a huge gap that can't be closed. This is where I don't know the exact.
constructor
08-18-23, 11:05
It's an uphill battle that most don't want to fight in the first place. I wish someone can redesign the extension and open source his work.
I also don't know how much potential there is under the current design, especially comparing to others. IF (big if) LMT's work can easily match Knights and other service rifles (AUG, G36/SCAR...), then it's not a huge gap that can't be closed. This is where I don't know the exact.
If you are talking about changing things for the military I wouldn't waste another minute. They give all the contracts to certain companies for a reason. If you come up with a better mouse trap they will steal it from you and give the design to a company they "work" with. I spent 4-5 years trying to show the military that the performance the 6.8 had was there IF everyone would just make the barrels correctly. I spent apx $40,000 in 2007 testing the 6.8 with every barrel configuration I could come up with, every powder and bullet combination and test results to prove the performance difference. As far as the military was concerned it was a complete waste but I sold a crap load of 6.8s to the public over the next 10 years. I have heard from several companies in the business who have the similar stories...don't waste your time trying to sell anything to the military.
ETA- I wasn't actually trying to sell product to the military, I was going to give them the info if they would just make the barrels correctly and take another look at the performance of the 6.8.
If you are talking about changing things for the military I wouldn't waste another minute. They give all the contracts to certain companies for a reason. If you come up with a better mouse trap they will steal it from you and give the design to a company they "work" with. I spent 4-5 years trying to show the military that the performance the 6.8 had was there IF everyone would just make the barrels correctly. I spent apx $40,000 in 2007 testing the 6.8 with every barrel configuration I could come up with, every powder and bullet combination and test results to prove the performance difference. As far as the military was concerned it was a complete waste but I sold a crap load of 6.8s to the public over the next 10 years. I have heard from several companies in the business who have the similar stories...don't waste your time trying to sell anything to the military.
ETA- I wasn't actually trying to sell product to the military, I was going to give them the info if they would just make the barrels correctly and take another look at the performance of the 6.8.
Yeah I doubt I want to do something for the bureaucracy. I just want to see how the XM7 turns out.
I was thinking doing what Glock has been doing, steady improvements over generations, and this time get a solid extension design that can lasts decades. This time we should have someone open-source the work, and if you really want to make some cash, I believe it's still possible under some CC licenses. People can use it, they just need to credit your name and pay a small fee.
Speaking of which, I think LMT's 6.8 bolts aren't particularly designed like their 5.56s.
With the Army, timing is everything.
In 2006, the Army was in the process of trying to convince everyone the M4 carbine with M855 ammunition was not an unreliable piece of junk than shot ammunition that just bounced off car windows. That would be the absolute wrong time to try and get them to acknowledge there was something even marginally better, let alone significantly better.
Fast forward ten years, and all the politicians have forgotten all of the 2005 and 2006 Congressional reports on M4 lethality, and they are actively looking for something better.
Several years ago Cris Murray(AMU) contacted me about making some test bolts to convert a MG42 to his new 7mmUIAC caliber. His design which I am sure is the normal MG42 design had 5 big lugs. After making them and holding them up to an AR15 bolt they were massive. IF anyone/everyone was agreeable to changing the barrel extension the sky is the limit.
If we are thinking about the same MG-42, changing from the locking rollers to a multi-lug, rotating bolt would have been a major alteration to the design.
http://thinlineweapons.com/MG42/images/MG42/oldbolt.jpg
https://i.ytimg.com/vi/BERGobm537A/mqdefault.jpg
Compared to the rotating bolt design of the MG-34:
https://i.ytimg.com/vi/i9A_zV7tUF4/maxresdefault.jpg
constructor
08-18-23, 16:32
If we are thinking about the same MG-42, changing from the locking rollers to a multi-lug, rotating bolt would have been a major alteration to the design.
http://thinlineweapons.com/MG42/images/MG42/oldbolt.jpg
https://i.ytimg.com/vi/BERGobm537A/mqdefault.jpg
Compared to the rotating bolt design of the MG-34:
https://i.ytimg.com/vi/i9A_zV7tUF4/maxresdefault.jpg
Not even close. He was designing a lighter weight GPMG to replace the 240 and said he was converting a MG42.
I know he had already built an AR10 in 7mmUIAC to test the performance of the cartridge and was wanting to build a FA mg to show what it would do as a belt fed.
https://www.thefirearmblog.com/blog/2010/04/07/7x46mm-uiac-universal-intermediate-assault-cartridge/
https://www.m4carbine.net/showthread.php?43479-News-on-7x46mm-Murray-cartridge
I've looked around and don't see any bolts that look like the ones I made. They say he was working on a PKM and he was in the sand box so it could be something found on the ground over there or something they had in inventory. It wasn't an AR10 bolt bolt, was longer than an AR10, 5 lug but closest to an AR bolt than anything else I have seen. Was not a MK48, Mk46, m249, M60, SCAR17.
That would have been interesting. Did a prototype ever get made?
Although, one thing I can say is designing links is one of those things that looks simple from the outside, but becomes a nasty can of worms when you try to do it. There was a lot of effort into what would be the M27 link, despite it looking like "just" an M13 scaled down.
10 to 12 rpm = one round every 5 to 6 seconds, which is the maximum sustained rate of fire.
120 to 150 rpm is a 3 to 5 round burst every three to four seconds.
It's enough to get the barrel up to about 500 to 600 degrees F after 120 rounds.
I'm just wondering whether the above mentioned firing schedule was for a different test than the US Army's 2007 baseline assessment for reliability for the M4? IIRC, you said that the 2007 baseline assessment used the following firing schedule:
120 round cycles with two 30-round magazines shot in bursts and two 30-round mags shot in semi-auto.
semi-auto mags: 1 round every second
burst mags: 3 to 5 rounds every 5 seconds for full automatic weapons and 3 rounds every 5 seconds for 3-round burst weapons.
I'm just wondering whether the above mentioned firing schedule was for a different test than the US Army's 2007 baseline assessment for reliability for the M4? IIRC, you said that the 2007 baseline assessment used the following firing schedule:
120 round cycles with two 30-round magazines shot in bursts and two 30-round mags shot in semi-auto.
semi-auto mags: 1 round every second
burst mags: 3 to 5 rounds every 5 seconds for full automatic weapons and 3 rounds every 5 seconds for 3-round burst weapons.
1 round every second is way too fast, I must have mistyped, According to the TOP, you should not exceed the maximum sustained rate of fire.
1 round every second is way too fast, I must have mistyped, According to the TOP, you should not exceed the maximum sustained rate of fire.
Thanks for the clarification and no worries. May I ask which TOP you are referring to? The version of TOP 3-2-045 that's available online says to fire the two semi-auto mags at a rate of 1 shot per second and the remaining mags in 3-5 round bursts at approximately 85 rpm.
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