View Full Version : Best piston conversion made so far?
Rauch Tactical
08-27-10, 17:53
Anyone know what conversion is considered the best example to date?
Magic_Salad0892
08-27-10, 19:44
The Adams kit is considered the ''best''.
I say that in quotes because they are all overgassed, and generally more risk than gain. Learn to take care of the DI system and it'll treat you better than you could ever treat it. I know from experience. (Having owned multiple LWRCi rifles. Even if they weren't conversions.)
If you're going the GP route (which is awesome too!) then buy an LWRCi, or LMT. Two systems that were designed to work as a piston AR.
(IE: proper gas port sizes, well designed carriers, etc.)
Plus, less reciprocating mass = more accuracy. Less recoil, less crap to fall apart, etc.
Robb Jensen
08-27-10, 19:47
AK-47 and the FAL are the best piston guns made IMHO.
Magic_Salad0892
08-27-10, 19:50
Add the Galil to that list.
He's right. Completely right.
JR TACTICAL
08-27-10, 20:57
Adams Arms are great, I personally have done 5 conversions to rifles I have owned and 3 to customers of mine. They work great, keep the inside of the rifle clean and cool (just as advertised) I feel spoiled because it runs so clean there is just no cleaning required after shooting.Adams Arms actually says there is no need to clean the system until 1000 rounds get run through the system.as far as overgased, maybe??? Just from experience, the buffer just gets beat
How do you fix that???
I put a wolff extra power spring in the buffer tube and an H buffer and that solved the problem.
I highly recommend the adams arms piston system if you are looking to convert your current DI system. but I agree LWRC and LMT make great piston guns if your in the market for a new AR
Adams Arms are great, I personally have done 5 conversions to rifles I have owned and 3 to customers of mine. They work great, keep the inside of the rifle clean and cool (just as advertised) I feel spoiled because it runs so clean there is just no cleaning required after shooting.Adams Arms actually says there is no need to clean the system until 1000 rounds get run through the system.as far as overgased, maybe??? Just from experience, the buffer just gets beat
How do you fix that???
I put a wolff extra power spring in the buffer tube and an H buffer and that solved the problem.
I highly recommend the adams arms piston system if you are looking to convert your current DI system. but I agree LWRC and LMT make great piston guns if your in the market for a new AR
so a spring and a buffer fixed this?
Ok, so I got a DD M4V2 Carbine, I replaced the standard D.I. system with the Adam Arms Piston System(that thing is sweet BTW) anyway, I have noticed when I pull the charging it sticks alittle, upon inspection when I looked at the charging handle and noticed no unusual ware so I pulled the buffer and spring and noticed that the carrier is rubbing on the bottom of the buffer tube on the inside???
Does anyone know if there is a fix for this? I was thinking about replacing the Buffer with an H-Buffer and I recently ordered a Wolff extra power spring because that piston system has just been abusing that stock buffer spring. I dont know if that alone will fix it. I had a buddy suggest ordering a Milspec buttstock assembly(mine is a Rock River Arms Commercial I built the lower from scratch) Any Thoughts???
How does the PWS system shape up in the real world ? I think the Addax system was originally based on that ?
JR TACTICAL
08-27-10, 23:08
so a spring and a buffer fixed this?
yeah it did actually i talked to an armorer i know and he suggested this it did the trick
justin_247
08-28-10, 10:46
My understanding is that Adams Arms modified their bolt carrier to tighter tolerances and that, in combination with a different buffer spring, eliminates the carrier tilt problem. I have no experience with this at all and this is based simply upon what I've read, so don't quote me on it.
I'm not entirely sure if this solved the problem in the long run, either, since it seems that most people who have the AA kits installed are hobby shooters who haven't put many rounds downrange with their rifles and, thus, we know little about the long-term effectiveness of this "fix." Additionally, I'm also not sure if machining to tighter tolerances is necessarily a good thing, and may well create more unintended problems.
There are, of course, modified buffers you can buy that have a notch that goes into the bolt carrier. One can see how this, too, may create more problems that it fixes.
pleaforwar
08-28-10, 13:16
How does the PWS system shape up in the real world ? I think the Addax system was originally based on that ?
Yes, Addax builds their ATAC uppers with the PWS long-stroke piston system.
Addax is also planning on releasing a new line of uppers that utilizes their own piston system.
snakedoctor
08-28-10, 20:51
AK-47 and the FAL are the best piston guns made IMHO.
What about the H&K G36 and H&K 416
I may grant the G36 in with the AK and FN, but not the 416...
Long story made short, don't do pistons in a system not designed initially for the system
Rauch Tactical
08-28-10, 21:49
What about the H&K G36 and H&K 416
What about staying on target? :D
So any long term reports of the Adams with better spring etc?
Magic_Salad0892
08-29-10, 00:44
I may grant the G36 in with the AK and FN, but not the 416...
Long story made short, don't do pistons in a system not designed initially for the system
Not that I'm in mad love with the 416, but why don't you like the system?
variablebinary
08-29-10, 01:08
I personally don't see the 416 as just another conversion, even if it has some AR15 commonality.
Magic_Salad0892
08-29-10, 01:24
Not that I know much about the design, other than some pictures of the internals, but I don't see anything it does that the LWRCi, or LMT offerings can't do.
variablebinary
08-29-10, 01:32
Not that I know much about the design, other than some pictures of the internals, but I don't see anything it does that the LWRCi, or LMT offerings can't do.
It's not an issue of mere function and capability
In the old days LWRC offered conversions for direct gas guns. If you sent HK a direct gas upper, it would be impossible to convert it into an HK416
Magic_Salad0892
08-29-10, 01:40
Back when LWRCi was Leitner Wise?
LWRCi piston guns are designed as piston guns. (I know. I've tried to drop in parts with an M6A1. D: )
variablebinary
08-29-10, 02:00
Back when LWRCi was Leitner Wise?
LWRCi piston guns are designed as piston guns. (I know. I've tried to drop in parts with an M6A1. D: )
It wasn't a drop it. It required some effort and calibration, but you could still send in a Colt, RRA, DPMS, or whatever and have the LWRC piston installed.
Impossible for an HK416
JR TACTICAL
08-29-10, 02:37
Got no long term results with the extra power spirng and buffer, only got like 250 down range with the stuff. But I will say the spring helps with recoil and the H buffer is not taking as much abuse, just normal ware. I would recommend getting one if your thinking about it you will be impressed:D
Magic_Salad0892
08-29-10, 03:20
It wasn't a drop it. It required some effort and calibration, but you could still send in a Colt, RRA, DPMS, or whatever and have the LWRC piston installed.
Impossible for an HK416
Thanks for the info.
BTW: Are you only using RRA, and DPMS as examples because LWRCi is the only service that could fix that crap?
variablebinary
08-29-10, 03:58
Thanks for the info.
BTW: Are you only using RRA, and DPMS as examples because LWRCi is the only service that could fix that crap?
I just chose the brands at random.
I decided on a piston rifle myself, did some research and found LWRCI to be the best IMO. Don't trust conversions, nor are the bugs worked out.
It wasn't a drop it. It required some effort and calibration, but you could still send in a Colt, RRA, DPMS, or whatever and have the LWRC piston installed.
Impossible for an HK416
Actually wery first take on HK416 (way before it was HK416 or even HKM4) was an factory upgrade for Colt M4. It was supposed to work the way HK did with SA80 -> complete rifles should be send to HK factory, where they would be converted into upgraded version. Basically what was supposed to remain intact was lower (upper were to be machined to work with specially designed FF quad rail handguard and to accept op-rod bushing) with fire control group (but with new buffer and spring). As this become un-feasible (sending US Govt weapons to Germany for processing) HK added new, own upper receiver and made complete conversion kit of proprietary upper plus new buffer and recoil spring and magazine as "upgrade" kit for Colt M4. Rest is history.
But yes, HK416 is not conversion kit for "regular AR-15" that can be made on user or even gunsmith level. Only upper part that is intact and exchangeable with AR-15 is charging handle, firing pin retaining pin and maybe bolt cam pin.
Basically it's G36 with M4 ergonomy - for me, suffering bouth of BRD and HKool-Aid addiction - 2in1 :D
Magic_Salad0892
08-30-10, 05:44
I too suffer from HKool-Aid. :cool:
Robb Jensen
08-30-10, 06:17
If you understand completely how the bolt operates in a DI gun (AR15 platform) you will understand why the piston in the AR platform is a very bad idea.
And by operates I don't me well it just gets gas to the bolt via a gas tube there a bit more to it than that.
If you understand completely how the bolt operates in a DI gun (AR15 platform) you will understand why the piston in the AR platform is a very bad idea.
And by operates I don't me well it just gets gas to the bolt via a gas tube there a bit more to it than that.
Preach it brother.
If you look at the DI system, for which the weapon platform was designed, you get a recoil impulse straight back, the gasses both pressurise the bolt against the barrel reducing the load on the lugs, and push the carrier backward in a rearward motion inline with the bore and receiver extension (buffer tube).
Piston guns in a M16FOW style do not do that.
Guns specifically designed as pistons (FN Fal, AK-47, XM-8, G36, AR-18, SCAR L and H etc) have rails to guide the bolt as the piston impacts the bolt carrier off axis to the bore. Also look at the lugs on the Ak bolt...
That information would imply that LWRC bolts should have shearing problems with their lugs. Are there any data supporting that? Have LWRCs been around long enough to know?
I only have a sample size of one but my Adams equipped sbr doesn't have hardly any wear on the bolt. It does have a spring in the carrier to simulate gas pressure in the carrier and to aid in avoiding bolt wear and shearing of the lugs.
I also don't have any issues with it tearing up the buffer or tube. Running an h buffer with standard spring and the Adams bolt carrier.
It does have negatives too. It adds weight to the end of the rifle. I notice it makes my 10.5 move like one of my 16" rifles. It is really noticeable. The recoil impulse is much stronger and sharper. Not enough to make a difference but it is there.
Again this is only a sample size of one rifle so it is definitely not a definitive case study on piston equipped AR15s
I have almost 9k through it so far and I can't say I would buy another one, but I am certainly not disappointed by any means.
Mike
Guns specifically designed as pistons (FN Fal, AK-47, XM-8, G36, AR-18, SCAR L and H etc) have rails to guide the bolt as the piston impacts the bolt carrier off axis to the bore. Also look at the lugs on the Ak bolt...
Look at the lugs on HK G36 or Steyr AUG bolt. And they seem to take loads of chamber pressure quite good. So maybe this is not a problem here?
BTW1 There is no free lunches: relocating gas piston and chamber from inside bolt carrier to gas block in AR15 has its benefit, but has downsides as well. That's why top 3Gun/UPSPSA/IPSC rifles shooters will not equip their sporting equipment with gas piston conversion any time soon, while some warriors would like to have their work tools to be this way ASAP.
BTW2 This thread was more about what conversion kit is best, not about if piston conversion is worth anything in firs place. We are drifting there into non-solvable discussion -> some like that other will die for other :rolleyes:
justin_247
08-30-10, 09:44
While the AR was certainly not designed for piston systems, I do think it's interesting that the Colt M5 / APC / LE1020 utilized a piston system very similar to some of the aftermarket piston modifications.
I still think it's a bit ghetto, especially when compared to the ACR, G36, and XCR systems.
That information would imply that LWRC bolts should have shearing problems with their lugs. Are there any data supporting that? Have LWRCs been around long enough to know?
Generally a piston gun receiver will end up taking the shock/load. One reason some piston guns receivers crack before the bolt does.
You can make a bolt out of a stronger and more resiliant material, but that impact is still right back into the barrel extension and it gets transfered into the upper.
No free lunch.
I didn't think about stresses endured by the receiver. I'll have to keep an eye on that.
Mike
Generally a piston gun receiver will end up taking the shock/load. One reason some piston guns receivers crack before the bolt does.
You can make a bolt out of a stronger and more resiliant material, but that impact is still right back into the barrel extension and it gets transfered into the upper.
No free lunch.
I could see off-axis impulse putting some stressors on the upper, although I would think the majority of it would be transfered to the buffer/spring. Your response is very thought-provoking and much appreciated.
Preach it brother.
If you look at the DI system, for which the weapon platform was designed, you get a recoil impulse straight back, the gasses both pressurise the bolt against the barrel reducing the load on the lugs, and push the carrier backward in a rearward motion inline with the bore and receiver extension (buffer tube).
Piston guns in a M16FOW style do not do that.
Guns specifically designed as pistons (FN Fal, AK-47, XM-8, G36, AR-18, SCAR L and H etc) have rails to guide the bolt as the piston impacts the bolt carrier off axis to the bore. Also look at the lugs on the Ak bolt...
the reduction in load on the bolts lugs, assuming it was possible which it is not, is about the same as a mouse reducing the pressure of an elephant's foot on the ground. there is zero forward movement of the bolt because you have the case absorbing the headspace and 27k psi pushing the bolt backwards.
you do not see premature bolt failures in any other piston operated multi-lugged, rotating bolt weapons.
Keep that opinion :rolleyes:
until someone demonstrates otherwise, i will.
That information would imply that LWRC bolts should have shearing problems with their lugs. Are there any data supporting that? Have LWRCs been around long enough to know?
Gas piston AR15s are harder on the bolt lugs than DI AR15s.
In a piston AR15, there is no gas force pushing the bolt foward, allowing pressure to come off the lugs and have the bolt unlock.
In a piston AR15, the lugs do a "hard" unlock, grinding against the chamber extension lugs.
until someone demonstrates otherwise, i will.
The bolt is not being push back in an AR-15, it is being pushed foward relative to the movement of the carrier.
I can't wait to not own a piston AR15.
Look at the people that buy a ruger SR556, sig 516, LWRC, etc. Look who these guns are marketed to. They are a bunch of wannabes or bubbas in sporting goods stores.
Be around the firearms industry enough and you will figure this out.
No need for anyone to be an asshat... people all too frequently forget that it's not the tool, but the one who wields it that generally dictates a positive outcome (for said individual). Many well equipped soldiers from all over the world have been uncomfortably surprised (and worse) by peoples with crap gear but a life time of fighting experience.
I find gear whores all the way to "tenured" Instructors woefully too centered on what they "think" is the best for the masses... vs concentrating on what works for the individual, much less just "for" the individual.
Granted, for a short moment I had an interest in piston guns... having a manufacturing back ground, I soon talked myself out of it due to the compromises not being in line with my mission. That's NOT to say it may not be within the parameters of others.
With that said, this thread is about what is the "best" conversion made... not the merits whether it's worth it in the first place.
The bolt is not being push back in an AR-15, it is being pushed foward relative to the movement of the carrier.
Stop making sense Scott...
:haha:
I mean just because he does not understand the operating principles of the M16FOW makes is not so right?
Magic_Salad0892
09-08-10, 03:45
Would you say the HK-416 and LWRC offering are marketed to bubba shooters?
Doesn't LMT have a military contract as well for the MRP Piston?
Gas piston AR15s are harder on the bolt lugs than DI AR15s.
In a piston AR15, there is no gas force pushing the bolt foward, allowing pressure to come off the lugs and have the bolt unlock.
In a piston AR15, the lugs do a "hard" unlock, grinding against the chamber extension lugs.
citations please. understand, i'm not trying to be argumentative but blanket statements without support are not helpful.
Thomas M-4
09-08-10, 08:14
Would you say the HK-416 and LWRC offering are marketed to bubba shooters?
Doesn't LMT have a military contract as well for the MRP Piston?
LWRC bubba shooter yes.
LMT MRP what contract?
HK-416 Is the only piston AR I would consider properly designed [ look at the the design you don't see DI parts in it].
Pretty sad state of affairs when there are third party aftermarket manufactures making widgets to cover up the short cumming of another aftermarket part.
LWRC bubba shooter yes.
LMT MRP what contract?
HK-416 Is the only piston AR I would consider properly designed [ look at the the design you don't see DI parts in it].
Pretty sad state of affairs when there are third party aftermarket manufactures making widgets to cover up the short cumming of another aftermarket part.
I pretty much agree with this.
The only piston AR15 that I will ever own will be HK416s for my reference collection. It will not be used, just collected.
citations please. understand, i'm not trying to be argumentative but blanket statements without support are not helpful.
What do you need a citation for? Anybody that is mechanically inclinded can clearly see how it works and what we are talking about.
citations please. understand, i'm not trying to be argumentative but blanket statements without support are not helpful.
Cite me.
Your getting a major fail in understanding of the operation of the M16FOW.
Gas is pushed down the gas tube, this also compresses the air inside the tube before firing. The air and then gas enter the carrier key and are deflected into the bolt carrier exanding to push against the bolt (hence pushing the bolt against the face of the breach and reducing the load on the locking lugs of the barrel extension and the bolt).
The carrier starts to move due to the gas pressue and unlocks the bolt via the cam pin while pressure is decreasing.
Not of that happens in a M16 piston gun. Offaxis forces smash the carrier rearward, and the bolt unlocks while pressure is exterted on the rear of the bolt lugs and forward face of the barrel extension.
If I was not in Va. right now, I could draw you a clear picture in Corel explaining this.
not quite accurate in your description of the operation as the first movement of the carrier is rearwards before the cam pin starts to rotate the bolt for the unlocking phase by which time the energy in the gas has started to overcome the mass of the bolt carrier, buffer and action spring. everything is moving backwards.
the distance between the back of the lugs on the barrel extension and the breach face is 0.287" and bolts are generally held to around 0.279" so with an empty chamber you have around 0.008" of clearance but once a cartridge is in there this is reduced.
as we now know that the carrier has started moving rewards pulling on the bolt before the bolt begins to turn; there is still residual pressure in the chamber pushing on the bolt face and the bolt extractor is pulling the empty case from the chamber, how can the bolt move forward? i just don't see how from a simple physics perspective that it is possible, that's my question.
think of it this way, does repeated dry cycling of the weapon cause lug damage?
this is where i have the problem getting what is being stated as the m16fow is unique in its operation yet other multi-lug rotating bolt designs using mechanical action to unlock (i.e. op-rod) do not suffer premature bolt or lug wear. while you cite off-axis forces, these are not unique to the op-rod driven m16fow, the stg44 had much greater off-axis forces and while the bolt design is different, it does not suffer lug damage during operation.
in terms of citations i was referring to documented examples of bolt lug wear; harder unlocking etc in op-rod driven weapons.
that's all
...The carrier starts to move due to the gas pressue and unlocks the bolt via the cam pin while pressure is decreasing.
Very simply put: The same amount of pressure used to push the bolt carrier to the rear is pushing the bolt forward, until the bolt unlocks and the pressure is vented out the side of the carrier. Then the momentum of the carrier continues the cycle.
William B.
09-08-10, 15:50
Cite me.
Your getting a major fail in understanding of the operation of the M16FOW.
Gas is pushed down the gas tube, this also compresses the air inside the tube before firing. The air and then gas enter the carrier key and are deflected into the bolt carrier exanding to push against the bolt (hence pushing the bolt against the face of the breach and reducing the load on the locking lugs of the barrel extension and the bolt).
The carrier starts to move due to the gas pressue and unlocks the bolt via the cam pin while pressure is decreasing.
Not of that happens in a M16 piston gun. Offaxis forces smash the carrier rearward, and the bolt unlocks while pressure is exterted on the rear of the bolt lugs and forward face of the barrel extension.
If I was not in Va. right now, I could draw you a clear picture in Corel explaining this.
I remember reading an interview with Reed Knight a few years ago in Small Arms Review where he said basically the same thing.
What good is a piston-driven AR if its cycle of operation is bad for it?
thopkins22
09-08-10, 15:52
think of it this way, does repeated dry cycling of the weapon cause lug damage?
Because people are able to cycle it as fast as the gas pressure right?
And you work for which top of the line firearm manufacturer?:confused:
Very simply put: The same amount of pressure used to push the bolt carrier to the rear is pushing the bolt forward, until the bolt unlocks and the pressure is vented out the side of the carrier. Then the momentum of the carrier continues the cycle.
yes of course, but the bolt is also being pushed rearward by chamber pressure and is captured between the breach face and barrel extension which is why the carrier moves rearwards; otherwise nothing would happen.
of course what we are discussing happens over a very short period of time and i'll have to do the math but i suspect that the chamber pressures are still relatively high as the carrier begins to pressurize.
i don't see the need for sarcasm to a legitimate question.
...by which time the energy in the gas has started to overcome the mass of the bolt carrier, buffer and action spring. everything is moving backwards.
The bolt does not move backwards until the cam pin pulls it, that is after the bolt has unlocked.
...as we now know that the carrier has started moving rewards pulling on the bolt before the bolt begins to turn...
No, think of it this way: The carrier is pushing off the bolt until the cam pin gets to the end of the cam pin slot.
The bolt does not have to be captured between the breach and barrel extension, it just pushes off the breech.
thanks todd, and you are correct, the carrier is pushing off the bolt which is for all intents and purposes stationary.
the problem i have is that the volume in the carrier, the surface area at the rear of the bolt and the gas pressure in the carrier are all insufficient to have any real effect on the rearward pressure on the bolt lugs.
the cam way controls the timing and as the carrier pressurizes it moves the carrier directly backwards for 1/8" before the cam path starts to rotate the bolt and unlock it. at this point the chamber pressures are beginning to reduce (if they weren't the bolt would not unlock) and the bolt is turning before being withdrawn.
this is really more of a technical issue rather than a general discussion and i apologize for the thread hyjack; i need to run some calculations.
I can't wait to not own a piston AR15.
Look at the people that buy a ruger SR556, sig 516, LWRC, etc. Look who these guns are marketed to. They are a bunch of wannabes or bubbas in sporting goods stores.
Be around the firearms industry enough and you will figure this out.
Where is your ring leader?
LWRC has been mentioned about 20 times, already. He's falling behind.
This place reminds me of Arfcom sometimes. :rolleyes:
-Vic
The_Hammer_Man
09-08-10, 20:50
Anyone know what conversion is considered the best example to date?
In descending order of my PERSONAL preferences in aftermarket piston drives.
Retrofit kits:
1) Osprey Defense (www.gaspiston.com) is my person fave for alot of reasons. The primary one being reliability. After installation in my first carbine conversion awhile back it's just been running and running. (over 5k rounds through it w/o a hiccup related to the piston conversion.) It's available in carbine/middie and rifle lengths.
2)Ares Defense: Possibly the most rugged retrofit kit I've ever worked with. This thing will take a pounding and still work! Currently at over 11k round through a full auto carbine that I built for a customer. The only downside to the setup is that is available only in carbine length. (yes, I've nagged at them via email about getting me a middie drive rod.. but no joy yet.)
Build Kits: (ie, Piston conversions utilized during the building,not retrofitting of a rifle)
Adams Arms: I have to agree with most of the people I've talked to about this that AA does make a nice setup. Even if it is heavier then it needs to be and overgassed like used car salesman on a tear! Reliable and easy to maintain. (Get a spare parts kit for it though. Mine tends to eat springs)
CMMG: Very reliable and nearly a carbon copy of the AA system with small differences. No noticeable difference in performance. (If you have emperical , not anecdotal, evidence to the contrary DO post!)
Proprietary Piston Systems: (piston systems that are part of the original design of a particular manufacturers weapon system)
Personal Faves,
POF: built like a tank and reliable.
PWS: same as above but a bit less easy to live with (for me! not YOU!) so if you own one please do not think I'm taking shots at you sacred cow. This is a personal preference.
Robinson Arms
Before anyone starts yapping bout the ACR and other great weapon systems out there let me remind you that this is from my PERSONAL experience!. I do not own an ACR yet or any of the other rather expensive options,like the FN SCAR, open to us these days. This will probably change but not anytime soon.
the problem i have is that the volume in the carrier, the surface area at the rear of the bolt and the gas pressure in the carrier are all insufficient to have any real effect on the rearward pressure on the bolt lugs.
This is exatly my tought. I'm not going to question experienced proffesionals, but I want to present my logic here:
NATO proofing for 5.56x45 is for maximum pressure of 430 MPa (62,367 psi) (125% of normal pressure). I can't see gas pipe and pipe to gas key connection stand this pressure. Evidently pressure inside bolt carries is much lower. In fact gas port in barrel works as sort of "pressure divider". If we also would remember that bolt and carrier are under force of inertia that push them backwards from the begining of bullet movement (laws of phisics) then it's very unlikely that locking lugs are not working themselves on barrel extension lugs. In fact if this point of view would be correct locking lugs would not be needed there - if chamber pressure can keep bolt face in battery why use of rotating bolt with locked lugs?? It can be done (HK P7), but it's whole different story.
One way to see how it goes is to paint back of bolt lugs in DI, shoot 1 shot and see if paint is intact. Same in piston (with same paint!) and see how paint looks comparing to DI. I can't do this, as currenly I do not own DI. I know that this is very simple test, not scientific and barbarian in nature but doable without $1M worth of equipment :D But if someone is willing to make this test I will be very interested to see results.
Montrala, your cycle of operation is way off.
The gas tube does not see pressure until the bullet passes the gas port. The pressure at this point is much less than max chamber pressure.
The bolt lugs take the force of the cartridge firing, there is no force on the carrier from the bolt. The carrier is actually held forward from the rifle recoiling to the rear, an object at rest...
The carrier can only move to the rear by pushing off the bolt, thus the bolt is being pushed forward as hard as the carrier is being pushed to the rear.
The carrier can only move to the rear by pushing off the bolt, thus the bolt is being pushed forward as hard as the carrier is being pushed to the rear.
this would result in nothing happening. obviously the gas pressure in the carrier acts equally in both directions but as the bolt is mechanically retained in the barrel extension, with residual chamber pressure acting upon it, the gas pressure in the carrier takes the path of least resistance and the carrier moves to the rear. in doing so, it moves around 1/8th of an inch straight back (timing) before the cam pin starts to rotate along the cam path and unlock the bolt.
the gas pressure, volume and surface area within the carrier are all too small to overcome the bolt thrust generated.
Quote:
Originally Posted by Miale
think of it this way, does repeated dry cycling of the weapon cause lug damage?
Because people are able to cycle it as fast as the gas pressure right?
i should have explained above that for comparison i meant using the weapon without a gas system.
if the weapon is tuned and set up correctly, the amount of energy required to unlock the bolt and cycle the action is the same whether you do it manually or by using the gas system to operate the weapon. the difference is the speed at which that energy is delivered. when you cycle the bolt manually, you are using the same amount of energy but delivering it over a longer time period. if you assume that the weapon is gassed correctly and that energy levels are equal, then wear characteristics on component parts should be be similar (not identical) over time.
this does not take into account wear cause by impact forces in a short stroke piston, but one would hope that the manufacturers had got that right.
Thomas M-4
09-11-10, 10:29
[QUOTE=Miale;755663]this would result in nothing happening. obviously the gas pressure in the carrier acts equally in both directions but as the bolt is mechanically retained in the barrel extension, with residual chamber pressure acting upon it, the gas pressure in the carrier takes the path of least resistance and the carrier moves to the rear. in doing so, it moves around 1/8th of an inch straight back (timing) before the cam pin starts to rotate along the cam path and unlock the bolt.
You agree with gas pressure acting equally on the bolt and carrier even if the bolt is captured it still is being acted equally on. The gas is being feed into a chamber there is no path of least resistance until the ports on the carrier are exposed.
I would suggest you reread KevinB & ToddK posts over because somewhere something is not clicking with you.
the gas pressure, volume and surface area within the carrier are all too small to overcome the bolt thrust generated.
Pressure is the same in the chamber and the carrier when the gas system is pressurized.
this would result in nothing happening
When the bolt is unlocked the pressure is vented. The carrier is already moving to the rear and the carriers momentum pulls the bolt with it via the cam pin.
Robb Jensen
09-11-10, 13:00
montrala,
On direct impingement ARs upon firing as the bullet passes the gas port in the barrel gas volume travels down the gas tube and then starts to fill the chamber created between the bolt carrier and the bolt. This momentarily drives the bolt forward (carrier doesn't move yet) and keeps the bolt locked until the chamber pressure drops. Then once completely energized with gas volume the carrier moves rearward unlocking the bolt and bleeding off the excess gas through the side of the carrier. Then whole BCG group moves rearward and extraction and ejection occur.
This driving the bolt forward doesn't occur on any of the piston ARs because it's a mechanical impact on the carrier which sends the carrier rearward. This is likely the reason real piston gun designs like the AK etc have huge bolt lugs.
[QUOTE]
You agree with gas pressure acting equally on the bolt and carrier even if the bolt is captured it still is being acted equally on. The gas is being feed into a chamber there is no path of least resistance until the ports on the carrier are exposed.
I would suggest you reread KevinB & ToddK posts over because somewhere something is not clicking with you.
think about what you have written. the bolt cannot move as it is between the lugs and the breach, the carrier can because the spring and buffer allow it to. it's not that difficult to comprehend.
Pressure is the same in the chamber and the carrier when the gas system is pressurized.
When the bolt is unlocked the pressure is vented. The carrier is already moving to the rear and the carriers momentum pulls the bolt with it via the cam pin.
sorry todd and respectfully, the chamber pressure is still higher than the carrier when the the system is pressurized. it is however dropping at a faster rate due to gas flow dynamics through an open cylinder at the point.
Thomas M-4
09-13-10, 22:42
think about what you have written. the bolt cannot move as it is between the lugs and the breach, the carrier can because the spring and buffer allow it to. it's not that difficult to comprehend.
I have you need to reread KevinB post in particular this part
The air and then gas enter the carrier key and are deflected into the bolt carrier exanding to push against the bolt (hence pushing the bolt against the face of the breach and reducing the load on the locking lugs of the barrel extension and the bolt).
Key word being "reduced "
montrala,
On direct impingement ARs upon firing as the bullet passes the gas port in the barrel gas volume travels down the gas tube and then starts to fill the chamber created between the bolt carrier and the bolt. This momentarily drives the bolt forward (carrier doesn't move yet) and keeps the bolt locked until the chamber pressure drops. Then once completely energized with gas volume the carrier moves rearward unlocking the bolt and bleeding off the excess gas through the side of the carrier. Then whole BCG group moves rearward and extraction and ejection occur.
This driving the bolt forward doesn't occur on any of the piston ARs because it's a mechanical impact on the carrier which sends the carrier rearward. This is likely the reason real piston gun designs like the AK etc have huge bolt lugs.
wrong, sorry and once again respectfully, you are suggesting that the bolt is able to move forward against around 27,000 psi at that particular point in the cycle, it doesn't happen and can't in any way shape or form happen because the volume and surface area is too small and the gas pressure in the carrier is less than 1/27th of the residual chamber pressure.
the ak was designed in the mid 1940's and acted upon the technology of the time; to suggest that the only "real" piston guns have bolts that copy contemporary bolt-action guns from the turn of the century ignores the numerous multi-lug designs that followed the ak.
interestingly enough, check the respective surface areas of multi-lugged bolts versus two or three lug designs. strangely enough you will find that multi-lug designs such as stoner's have a greater surface area. go figure.
I have you need to reread KevinB post in particular this part
Key word being "reduced "
ok, so we reduce the pressure on the bolt lugs by say at best 900 to 1,200 psi, seriously, it's inconsequential.
do you seriously think that 1,200 psi can overcome a rearward force of 27,000 psi?
that's the only point i'm trying to make. there is no space within the breach/lug area to allow this to happen; there is insufficient surface area and pressure within the carrier to allow this to happen so how does it happen?
Thomas M-4
09-13-10, 23:47
But maile there is space between the front face of the bolt and the inside of the barrel extension. You can drop a bolt in and see for you self. If it had .000" clearance it would never run at least not past the first mag.
Most guys have already read this http://www.ar15barrels.com/prod/operation.shtml He talks about timing little bit more maybe it will help.
Has GotM4 stated earlier about the AK and in general piston system locking lugs being bigger the scar being a modern example.
Very simply put: The same amount of pressure used to push the bolt carrier to the rear is pushing the bolt forward, until the bolt unlocks and the pressure is vented out the side of the carrier. Then the momentum of the carrier continues the cycle.
In the case of the HK416, there's a firing pin spring which places forward tension on the bolt head, causing it to move into the chamber area during unlocking. Would this not alleviate any issues related to excessive force being applied to the lugs?
Another thought that comes to mind, what kind of round counts are we talking about with the 416's with cracked receivers?
Tspeis
The spring on the Hk416 is to reduce firing pin pressure on chambering, since the bolt is not slowed by the friction from the gas rings. It does nothing to hold the bolt against the face of the breech.
When I was in Europe a few months ago, two user groups where stating 3,500 rds suppressed receiver cracks.
But maile there is space between the front face of the bolt and the inside of the barrel extension. You can drop a bolt in and see for you self. If it had .000" clearance it would never run at least not past the first mag.
Most guys have already read this http://www.ar15barrels.com/prod/operation.shtml He talks about timing little bit more maybe it will help.
Has GotM4 stated earlier about the AK and in general piston system locking lugs being bigger the scar being a modern example.
correct. my earlier post called out the barrel extension dims and there is around .009" clearance, however once a cartridge case is inserted this is reduced further.
one additional thing to bear in mind is that the ar extracts with chamber pressure assistance so even in the final stage of the cycle there is still sufficient residual pressure in the chamber to kick the cartridge out. (there was an ndia briefing on this where two weapons were joined by gas tubes so that when one was fired, it would cycle the action of the other)
When I was in Europe a few months ago, two user groups where stating 3,500 rds suppressed receiver cracks.
Any details to support this claim, other that it is spreading bad PR about competitor without stating verificable facts? Your signature should oblige you to some level of professionalism there. Or is it just way of doing business?
BTW So finally it's not lugs on barrel extension or bolt that cracks due to piston but receiver? Good to know we are moving forward. Lower or upper?
The spring on the Hk416 is to reduce firing pin pressure on chambering, since the bolt is not slowed by the friction from the gas rings. It does nothing to hold the bolt against the face of the breech.
When I was in Europe a few months ago, two user groups where stating 3,500 rds suppressed receiver cracks.
My apologies, I should have been a bit more clear with my post. I know the purpose of the firing pin spring is to put rearward tension on the firing pin so it can reengage with the firing pin safety lever. However, if you remove the bolt group from a 416, you'll notice that the bolt head immediately springs forward upon removal. You're saying this would not act in a similar capacity to that of a DI bolt being pushed towards the breech during unlocking?
If I'm not mistaken, there's actually an aftermarket spring available for piston guns specifically for the purpose of reducing the force placed on the bolt lugs. Please don't take this post the wrong way, just trying to make sure I was clear.
Thanks!
Tspeis
The spring on the Hk416 is to reduce firing pin pressure on chambering, since the bolt is not slowed by the friction from the gas rings. It does nothing to hold the bolt against the face of the breech.
When I was in Europe a few months ago, two user groups where stating 3,500 rds suppressed receiver cracks.
A certain bearded instructor made the EXACT same comment last week. Including op rods flexing so hard they were sparking as they struck the barrel. I forayed into piston for a bit, and I enjoyed my PWS well enough, but I'm back to DI guns.
Any details to support this claim, other that it is spreading bad PR about competitor without stating verificable facts? Your signature should oblige you to some level of professionalism there. Or is it just way of doing business?
BTW So finally it's not lugs on barrel extension or bolt that cracks due to piston but receiver? Good to know we are moving forward. Lower or upper?
Montrala, you need to step back a bit. Kevin is both an Subject Matter Expert, Senior Staff, and I know he has used both HK 416's and KAC gear while deployed, prior to his working with KAC.
A certain bearded instructor made the EXACT same comment last week. Including op rods flexing so hard they were sparking as they struck the barrel. I forayed into piston for a bit, and I enjoyed my PWS well enough, but I'm back to DI guns.
Interestingly, I asked that beared expert at what point he had heard HK416s start to experience cracked receivers. He stated that some had experienced them at around 80K rounds. How many M4 receivers would last that long?
Heavy Metal
09-15-10, 20:43
The number I have heard for just the upper reciever on an AR is around 100K rounds.
First, I think for the money the average user is much better off with a top name DI AR, like a Colt, LMT, Daniel Defense, Bravo Company, etc.
When I was in Europe a few months ago, two user groups where stating 3,500 rds suppressed receiver cracks.
With all due respect, if that were a normal occurance with the HK416, I would think that certain units who spearheaded demand for the HK416 and have been using it the longest would have long since abandoned it or never adopted it in the first place.
I know there have been rumors on the Internet about them abandoning it, and as of several months ago I confirmed them not to be true. I spent quite a lot of time pursuing these rumors, and probably got myself on a goverment list or two.
I have about 4K rounds through mine, with no evidence of cracks. Maybe a thousand rounds were run through it supressed.
We also have SMEs like DOCGKR stating:
Some recent military shooting demonstrated that the HK416 exhibited substantially greater reliability and 3-4 times the durability of a Colt M4, with significantly less need for maintenance.
and Dano5326 writes:
The HK416 is a much cheaper weapons system when one considers the lifecycle cost on a high rd ct training (aka a training/demonstrator) weapon.
With the same rd ct, you will go through several M4A1 uppers before a 416 upper is wornout.
Robb Jensen
09-15-10, 21:07
Miale,
I share my knowledge here free of charge. You don't have to agree nor believe me with what I've seen and experienced. I personally don't care either way. Stay Safe.
Robb
I think Hk has the best Engineering department of any firearms company, so don't think I am bad mouthing them.
I've had Hk416's do well over 10k before with no issues. I know test guns that ran into the 30k's and higher.
I was asked for a number, and I repeated what was given to me.
I have no data to back that up, so take it for what its worth.
My favorite belt fed gun is the Hk21 so I'm not bashing Hk...
I think Hk has the best Engineering department of any firearms company, so don't think I am bad mouthing them.
I've had Hk416's do well over 10k before with no issues. I know test guns that ran into the 30k's and higher.
I was asked for a number, and I repeated what was given to me.
I have no data to back that up, so take it for what its worth.
My favorite belt fed gun is the Hk21 so I'm not bashing Hk...
I wonder if these user groups got a batch of guns with bad receivers? I don't want to speculate, but 3,500 rounds is just crazy.
Anyway, thank you for the info Kevin. Much appreciated as always.
Tspeis
IMO, the Barrett REC7 is the current "best in class"
Montrala, you need to step back a bit. Kevin is both an Subject Matter Expert, Senior Staff, and I know he has used both HK 416's and KAC gear while deployed, prior to his working with KAC.
I think we cleared this matter on PM with Kevin.
Sorry for late answer, spend some time in Belgrade, Serbia (it's strange to see big bulidings in center of european capital sity completelly deserted with huge gaps where bombs hit) lately and did not have time to follow forum.
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