View Full Version : Can you cite specific failures of piston AR's?
The_Biased_Observer
02-27-11, 18:27
I've read several threads here and other places where people claim having witnessed piston guns "failing" or "self destructing" but they usually make no other description of the failure. I'd like to see actual descriptions of parts or components that fail or break in the various piston designs. So the question is, have you seen or experience and actual parts breakage on a piston model AR? What part was it that broke? Any photos of the breakage would be fantastic.
Things like carrier tilt are not germane here unless they actually broke something as that issue seems to be fairly well remedied.
I'm wondering if descriptions of piston guns failing are due to other poor components (out of spec barrels, etc) making the gun fail or are actual breakage of parts?
Good topic, I'd be interested as well. Other than some abnormal wearing of receiver extensions due to tilt, I haven't seen any parts breakage reports either. As a piston owner (LMT) I've definitely paid lots of attention to the piston discussions and reports on the various boards.
M ine chronically brakes little holes in targets at 100 yards. But thats it?
Mine was attributed to the magazine, not the gun. Barrett 6.8 mags have a lip at the rear of the follower that my bolt catch had gotten underneath preventing me from stripping the magazine from the weapon, it happened enough I ordered a few C Products magazines and havent had an issue since.
The_Biased_Observer
02-28-11, 15:39
Hopefully a few who repeatedly poo-poo the piston guns will chime in at some point.
I don't own one so Im certainly not a koolaid drinker but find the idea a good one for guns with suppressors, I have very mediocre results with gas guns using a can. Reliability takes a nose dive in my experience.
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westcoastfrog
02-28-11, 17:59
My 416 had few issues but it did have a few. First issue was when a leg of my firing pin retaining cotter pin broke off and locked my bolt halfway back. Second i had a bolt prong sheer off on the non extractor side. I continued to shoot the gun for at least a couple of thousand rounds to see how it would do and it even continued to work after the second prong sheered off...third prong sheered off and gun became a bolt action. Justmy limited experience with the 416. Would still trust ,y life to it if parts weren't so hard to get....ultimately i decided that a well maintained di m4with plenty of replacement parts was a better fit for me than a high speed gun that i couldn't maintain properly in regards to parts.
I am confused. You had mediocre results with a piston gun and suppressor or a DI gun and suppresor?
Hopefully a few who repeatedly poo-poo the piston guns will chime in at some point.
I don't own one so Im certainly not a koolaid drinker but find the idea a good one for guns with suppressors, I have very mediocre results with gas guns using a can. Reliability takes a nose dive in my experience.
Sent from my DROIDX using Tapatalk
Carrier tilt is actually important. Tell me what happens to the bolt if the carrier is tilting downward into the lower receiver extension?
There are reports (I haven't seen one) of the bolt lugs cracking on some bolts.
I've read several threads here and other places where people claim having witnessed piston guns "failing" or "self destructing" but they usually make no other description of the failure. I'd like to see actual descriptions of parts or components that fail or break in the various piston designs. So the question is, have you seen or experience and actual parts breakage on a piston model AR? What part was it that broke? Any photos of the breakage would be fantastic.
Things like carrier tilt are not germane here unless they actually broke something as that issue seems to be fairly well remedied.
I'm wondering if descriptions of piston guns failing are due to other poor components (out of spec barrels, etc) making the gun fail or are actual breakage of parts?
I put an Osprey kit on one of my ARs , it's timed right with my barrel and it has been perfect. No tilt (comes with BC), only thing I notice is a weee more wear on the carrier key.
Some piston/ Bolt combo kits and complete rifles work better than others and wear less.
I don't own one so Im certainly not a koolaid drinker but find the idea a good one for guns with suppressors, I have very mediocre results with gas guns using a can. Reliability takes a nose dive in my experience.
I'm no expert, so wait to have this confirmed, however I'm fairly certain that a piston's place is on a 10.5" gun that simply wont stop short cycling, not necessarily a suppressed one. Here's a quote from an interview with John Noveske published on Defense Review:
"I only run the guns with suppressors for testing when I did my comparison, and with suppressors, direct-impingement and piston-operated were both very dirty, ’cause the blowback comes to the chamber, not the gas tube." - John Noveske
Full article: http://www.defensereview.com/noveske-rifleworks-n4-light-recce-carbine-john-noveske-interview-part-one/
I believe westcoastfrog is referring to the bolt lugs. I have *heard* of but never experienced any issues with bolt lugs on piston guns. I own an upper with a carbine-length Adams Arms system. What I've heard about bolt lugs shearing off has something to do with increased unlocking speeds and increased pressure per lug because of that. Whether or not there even is substantially increased pressure on the lugs and whether or not this pressure, if extant, would cause failure remains to be substantially evidenced as far as I know.
Edit: Oh yeah, and if the carrier's tilting... Cant be too good for the lugs, either...
What this thread may boil down to is that, although some piston-equipped ARs may function just fine... There's still no reason to use them over DI ARs.
I had a CMMG piston upper over a Rock River lower. One day at the range the weapon stopped feeding rounds. Basically it turned into a single shot AR. When I got home and disassembled the upper I found that the piston rod return spring had jumped over it's retainer therefore failing to push the piston back into it's bore for the next shot. It was at that point that I decided piston ARs were not for me. Didn't think to take photos. Sorry bout that, they would have been interesting to look at now.
Carrier tilt is actually important. Tell me what happens to the bolt if the carrier is tilting downward into the lower receiver extension?
There are reports (I haven't seen one) of the bolt lugs cracking on some bolts.
Thanks for posting this IG. What a shit storm I started at TOS when I mentioned this very point. It stands to reason that if the BCG is tilting at the rear it has to also be putting pressure at the bolt lugs and it's tail.
Carrier tilt is actually important. Tell me what happens to the bolt if the carrier is tilting downward into the lower receiver extension?
There are reports (I haven't seen one) of the bolt lugs cracking on some bolts.
I thought the carrier tilt problem can easily be solved? So besides carrier tilt what else is the problem?
My 416 had few issues but it did have a few. First issue was when a leg of my firing pin retaining cotter pin broke off and locked my bolt halfway back. Second i had a bolt prong sheer off on the non extractor side. I continued to shoot the gun for at least a couple of thousand rounds to see how it would do and it even continued to work after the second prong sheered off...third prong sheered off and gun became a bolt action. Justmy limited experience with the 416. Would still trust ,y life to it if parts weren't so hard to get....ultimately i decided that a well maintained di m4with plenty of replacement parts was a better fit for me than a high speed gun that i couldn't maintain properly in regards to parts.
Why the hell would you keep firing it after a bolt lug broke off? After TWO broke off?!? :blink:
I'd be more interested in actual account of WORKING PISTONS...
I wouldn't believe them.... but I'd be interested in the accounts. :D
Sttrongbow
02-28-11, 20:14
Carrier tilt is actually important. Tell me what happens to the bolt if the carrier is tilting downward into the lower receiver extension?
There are reports (I haven't seen one) of the bolt lugs cracking on some bolts.
Well, wear is only important if it contributes to a significant lessening of the life of the part, or leads to a specific failure.
And plenty of DI guns break bolt lugs....
Sttrongbow
02-28-11, 20:15
I'd be more interested in actual account of WORKING PISTONS...
I wouldn't believe them.... but I'd be interested in the accounts. :D
Sarcasm, I assume?
I have an LWRCi upper with a couple thousand trouble-free rounds through it....
The_Biased_Observer
02-28-11, 20:51
Carrier tilt is actually important. Tell me what happens to the bolt if the carrier is tilting downward into the lower receiver extension?
There are reports (I haven't seen one) of the bolt lugs cracking on some bolts.
Would the floating bolt "head" due to tolerances with the bolt ring OD, carrier ID and cam pin groove mitigate any effect of limited carrier tilt (use of anti tilt buffer) on the bolt lugs?
Bolt lugs also crack on gas guns, internal piston guns, direct impingement guns, whatever you want to call them.
But, the recoil impulse on a piston gun is certainly different and might be more severe due to the lack of a forward impulse from the gas operation.
Seriously? Think about this. If the rear of the carrier is tilting, that means that the front of the carrier (where the bolt is) is also tliting upwards which is going to put stress on the bolt as the carrier travels rearward and the bolt unlocks.
You're right about DI guns bolts breaking. Which is why you should be even more concerned.
Well, wear is only important if it contributes to a significant lessening of the life of the part, or leads to a specific failure.
And plenty of DI guns break bolt lugs....
Littlelebowski
02-28-11, 21:07
Robb Jensen has written on this site about Hk416s cracking receivers.
Sarcasm, I assume?
I have an LWRCi upper with a couple thousand trouble-free rounds through it....
Now you have done it. The mere mention of LWRCI sends Markm over the edge.
I have 3 piston guns in my stable - REPR, M6A2, and LMT MRP. All three are just as reliable as my other DI weapons.
The_Biased_Observer
02-28-11, 21:08
I'm no expert, so wait to have this confirmed, however I'm fairly certain that a piston's place is on a 10.5" gun that simply wont stop short cycling, not necessarily a suppressed one. Here's a quote from an interview with John Noveske published on Defense Review:
"I only run the guns with suppressors for testing when I did my comparison, and with suppressors, direct-impingement and piston-operated were both very dirty, ’cause the blowback comes to the chamber, not the gas tube." - John Noveske
Full article: http://www.defensereview.com/noveske-rifleworks-n4-light-recce-carbine-john-noveske-interview-part-one/
Using a suppressor on a gas gun is often cited as a cause for increased bolt speed (force) which can only come from increased gas tube pressure on a gas gun, no?
Use of a can lengthens the amount of time higher than ambient pressure remains in the barrel (and hence, gas tube) so it seems reasonable to say that the source of dirty overall is both from the barrel/chamber and gas tube. Obviously, the barrel will accomodate a lot more gas than the tube will in this environment and is connected directly to the chamber so maybe the amount from the tube can be considered negligible?
I guess my pipe dream of pistons being great for cans is busted. :suicide:
Hey OP, you don't expect to get many real answers do you?
Robb Jensen
02-28-11, 21:37
Yes:
HK...cracked upper receivers when shot hard suppressed. Firing pin safety failures. Broken bolts.
POF...highly worn receiver extensions which caused erratic bolt velocity which was causing failure to eject, failure to feed etc whenever the bolt carrier would get caught in the trough cause by carrier tilt. Cracked bolt, cracked log at top of bolt. Large amount of finish wear/gouging caused by front-top of bolt carrier dragging along the receiver bore as the carrier tilt. A temp fix is a new receiver extension and new upper receiver (two things that don't really wear out in DI guns by the way). One particular POF I've seen will not run on this one particular AR lower but on that same AR lower all DI uppers (7 different ones) worked just fine. Corrosive pitting of the gas piston and op rod. Broken bolt lug which got between the carrier and upper receiver and ruined the upper receiver which required a new receiver and new bolt.
early ARES....bent op rod in less than 600 rounds on full auto on a 11.5" upper, due to spigot coming lose after the gas tube roll pin 'exited stage left'.
LWRC...I've thus far fixed 4 lose barrel nuts, replaced heavy worn receiver extensions with this wear causing unusual stoppages (fixed with a new extension and anti-tilt buffer). Early ones had carrier keys coming lose before they key was integral to the carrier. On two early one I replaced two broken bolts (before Matech).
PWS...lose gas block (2nd gen after moving away from a pinned gas block to a set screw gas block). Newer pinned Diablo style is much better. 1st gen I had the piston (which is attached to the carrier) came lose but I caught it before it caused stoppages.
LMT...highly worn receiver extensions from carrier tilt causing unusual stoppages fixed with a new receiver extension and anti-tilt buffer. Lose barrels if not checked regularly.
So to summarize what I've said in the past, If Eugene Stoner wanted the AR to be a 'gas piston' design he would have made it that way from the get go. Trying to make the AR15 platform a piston gun is like Chevrolet back in the day trying to make a good diesel engine out of the small block 350 (5.7L) engines ...it didn't turn out to well.
Cagemonkey
03-01-11, 08:50
Well said. Did the PWS experience less problems and parts breakage due to the fact it is a long stroke piston op and probably has a lower BCG velocity? Or is this an incorrect assumption?
piston guns "failing" or "self destructing"
I bought a CMMG piston gun (gen 1) during the Obamamania rush when people, including me, were buying everything with a trigger. It was NIB of course.
Somewhere between the 10th and 20th shots of Federal XM193 ammo, the action locked up tight. TIGHT!! So I sent it back to CMMG. It was there a month or so and they sent it back as a Gen 2 gun. I could see that some parts were different while some, like the barrel, were the same. They did not charge for the repair. The gun did not come back with a work order that said what was wrong.
At that point I was spooked and sold the gun for a big loss. The new owner said he really liked it so maybe Gen 2 was the magic that it needed.
Yes:
HK...cracked upper receivers when shot hard suppressed. Firing pin safety failures. Broken bolts.
POF...highly worn receiver extensions which caused erratic bolt velocity which was causing failure to eject, failure to feed etc whenever the bolt carrier would get caught in the trough cause by carrier tilt. Cracked bolt, cracked log at top of bolt. Large amount of finish wear/gouging caused by front-top of bolt carrier dragging along the receiver bore as the carrier tilt. A temp fix is a new receiver extension and new upper receiver (two things that don't really wear out in DI guns by the way). One particular POF I've seen will not run on this one particular AR lower but on that same AR lower all DI uppers (7 different ones) worked just fine. Corrosive pitting of the gas piston and op rod. Broken bolt lug which got between the carrier and upper receiver and ruined the upper receiver which required a new receiver and new bolt.
early ARES....bent op rod in less than 600 rounds on full auto on a 11.5" upper, due to spigot coming lose after the gas tube roll pin 'exited stage left'.
LWRC...I've thus far fixed 4 lose barrel nuts, replaced heavy worn receiver extensions with this wear causing unusual stoppages (fixed with a new extension and anti-tilt buffer). Early ones had carrier keys coming lose before they key was integral to the carrier. On two early one I replaced two broken bolts (before Matech).
PWS...lose gas block (2nd gen after moving away from a pinned gas block to a set screw gas block). Newer pinned Diablo style is much better. 1st gen I had the piston (which is attached to the carrier) came lose but I caught it before it caused stoppages.
LMT...highly worn receiver extensions from carrier tilt causing unusual stoppages fixed with a new receiver extension and anti-tilt buffer. Lose barrels if not checked regularly.
So to summarize what I've said in the past, If Eugene Stoner wanted the AR to be a 'gas piston' design he would have made it that way from the get go. Trying to make the AR15 platform a piston gun is like Chevrolet back in the day trying to make a good diesel engine out of the small block 350 (5.7L) engines ...it didn't turn out to well.
Were these all your own personal guns or a mix of your guns and other peoples guns? What kind of round counts are we looking at also?
Robb Jensen
03-01-11, 09:41
Were these all your own personal guns or a mix of your guns and other peoples guns? What kind of round counts are we looking at also?
Both...guns I've seen, worked on, shot, owned, T&E'd. Some as little at 1-2K rounds on them some as much as 25K rounds.
leroyswift
03-01-11, 09:49
Yes:
HK...cracked upper receivers when shot hard suppressed. Firing pin safety failures. Broken bolts.
POF...highly worn receiver extensions which caused erratic bolt velocity which was causing failure to eject, failure to feed etc whenever the bolt carrier would get caught in the trough cause by carrier tilt. Cracked bolt, cracked log at top of bolt. Large amount of finish wear/gouging caused by front-top of bolt carrier dragging along the receiver bore as the carrier tilt. A temp fix is a new receiver extension and new upper receiver (two things that don't really wear out in DI guns by the way). One particular POF I've seen will not run on this one particular AR lower but on that same AR lower all DI uppers (7 different ones) worked just fine. Corrosive pitting of the gas piston and op rod. Broken bolt lug which got between the carrier and upper receiver and ruined the upper receiver which required a new receiver and new bolt.
early ARES....bent op rod in less than 600 rounds on full auto on a 11.5" upper, due to spigot coming lose after the gas tube roll pin 'exited stage left'.
LWRC...I've thus far fixed 4 lose barrel nuts, replaced heavy worn receiver extensions with this wear causing unusual stoppages (fixed with a new extension and anti-tilt buffer). Early ones had carrier keys coming lose before they key was integral to the carrier. On two early one I replaced two broken bolts (before Matech).
PWS...lose gas block (2nd gen after moving away from a pinned gas block to a set screw gas block). Newer pinned Diablo style is much better. 1st gen I had the piston (which is attached to the carrier) came lose but I caught it before it caused stoppages.
LMT...highly worn receiver extensions from carrier tilt causing unusual stoppages fixed with a new receiver extension and anti-tilt buffer. Lose barrels if not checked regularly.
So to summarize what I've said in the past, If Eugene Stoner wanted the AR to be a 'gas piston' design he would have made it that way from the get go. Trying to make the AR15 platform a piston gun is like Chevrolet back in the day trying to make a good diesel engine out of the small block 350 (5.7L) engines ...it didn't turn out to well.
+1 on the junky chevy diesels.Oh and trying to make the AR platform something it was never meant to be. People will never stop trying though.
Cincinnatus
03-01-11, 09:56
Robb has also shot and evaluated the Ruger piston AR, which experienced a great deal of carrier tilt and associated wear in the first 1,000 rds.
Doc Safari
03-01-11, 10:04
This is why I love this forum. You guys have saved me another thousand bucks by talking me out of a piston AR.
leroyswift
03-01-11, 10:19
I agree doc, I was going to order a kit from centerfire systems that was a cheap retrofit set up. save my money and buy cleaning supplies :D
Sttrongbow
03-01-11, 10:39
Seriously? Think about this. If the rear of the carrier is tilting, that means that the front of the carrier (where the bolt is) is also tliting upwards which is going to put stress on the bolt as the carrier travels rearward and the bolt unlocks.
You're right about DI guns bolts breaking. Which is why you should be even more concerned.
Yeah, seriously... I do think about this a lot. I'm a mechanical engineer, so thinking about this kind of stuff isn't alien to me. Wear is a problem ONLY if you can trace it to a specific issue. Machines wear. If you change the design of the machine it will wear DIFFERENTLY. A difference in wear isn't necessarily better or worse. It's different. You need more data to determine if wear is a problem.
And again, on the bolt lugs.... can you describe the actual stresses an strains on the lugs? How do they compare with the stresses placed on the lugs in a DI gun? I don't know, and I doubt anyone really does.
But I don't think there's an avalanche of data showing a problem in the piston guns. In fact, I'd say lower quality DI guns are a way worse problem for AR users.
Sttrongbow
03-01-11, 10:47
Using a suppressor on a gas gun is often cited as a cause for increased bolt speed (force) which can only come from increased gas tube pressure on a gas gun, no?
Use of a can lengthens the amount of time higher than ambient pressure remains in the barrel (and hence, gas tube) so it seems reasonable to say that the source of dirty overall is both from the barrel/chamber and gas tube. Obviously, the barrel will accomodate a lot more gas than the tube will in this environment and is connected directly to the chamber so maybe the amount from the tube can be considered negligible?
I guess my pipe dream of pistons being great for cans is busted. :suicide:
But the tube is open to the receiver and BCG and as soon as the bullet passes the gas port, there's gas and carbon in the receiver. The bolt doesn't unlock until after the bullet has left the barrel and the pressure has started to decrease. Once the bolt unlock and extraction begins, the residual pressure in the barrel will blow junk back into the receiver (whether Di or Piston), but at a lower pressure than what came in through the gas tube. Without doing more calculations than I care to, I can't tell you whether more junk in the receiver comes from the gas tube or the chamber, but my limited experience of cans on both piston and DI AR's tells me the DI puts more junk in the receiver than the piston AR.
However, both get pretty darned dirty with a can.
militarymoron
03-01-11, 10:48
PWS...lose gas block (2nd gen after moving away from a pinned gas block to a set screw gas block). Newer pinned Diablo style is much better. 1st gen I had the piston (which is attached to the carrier) came lose but I caught it before it caused stoppages.
my gen I PWS has an issue with the piston tube weld - but that was a proto and the design was changed to address that. no issues on the gen 2 (built by addax). the 'gen 3' is my addax-built PWS long-stroke 16" piston upper which i've been shooting since aug '09 and it's the upper i shoot the most (i also have about 10 other DI uppers to pick from). the two main reasons are that it's the easiest to clean out of all of them (both DI and piston), and it's also been very reliable through 5 or 6k rounds. i normally do a 15-20 min clean after each range session when shooting DI guns, but the addax reduces it to 5 mins with a bore snake and wipe down. less parts to clean than a DI gun (i don't really clean anything other than the bore - everything gets a wipe down vs a more thorough clean when i shoot DI guns - that's just me).
with the FRS anti-tilt buffer, there's no carrier-tilt wear in the buffer tube, and no more wear on the carrier bearing surfaces than a DI carrier. it has the spring-loaded bolt that puts a bit of pressure on it to keep it in the forward position and i believe that it helps with premature wear seen in some piston guns without it at the cam pin cutout in the upper receiver. it's a midlength, and shoots as soft as any other DI gun - even softer than some carbine gas systems.
for a recreational shooter like me not using cans or an SBR, it may offer no practical advantage over a DI upper, but i still reach for it more often than my other uppers.
my only concern is replacement parts if something breaks, since the system is non standard. other than that, it's been trouble-free for me.
Thomas M-4
03-01-11, 11:00
Yeah, seriously... I do think about this a lot. I'm a mechanical engineer, so thinking about this kind of stuff isn't alien to me. Wear is a problem ONLY if you can trace it to a specific issue. Machines wear. If you change the design of the machine it will wear DIFFERENTLY. A difference in wear isn't necessarily better or worse. It's different. You need more data to determine if wear is a problem.
And again, on the bolt lugs.... can you describe the actual stresses an strains on the lugs? How do they compare with the stresses placed on the lugs in a DI gun? I don't know, and I doubt anyone really does.
But I don't think there's an avalanche of data showing a problem in the piston guns. In fact, I'd say lower quality DI guns are a way worse problem for AR users.
The buffer tube was not designed to be a wear part.
If you look at every ground up piston design they have some form of rails that guide the carrier and stops carrier tilt. This is missing in the AR-15 design because it is unnecessary because there is no carrier tilt present in the DI system all forces are in line with the bore.
Robb Jensen
03-01-11, 11:47
Robb has also shot and evaluated the Ruger piston AR, which experienced a great deal of carrier tilt and associated wear in the first 1,000 rds.
Yeah I forgot to include that one.
Sttrongbow
03-01-11, 11:48
The buffer tube was not designed to be a wear part.
If you look at every ground up piston design they have some form of rails that guide the carrier and stops carrier tilt. This is missing in the AR-15 design because it is unnecessary because there is no carrier tilt present in the DI system all forces are in line with the bore.
I hear ya, but I add: What failure mode are you introducing? I haven't seen any significant evidence of one. The AR-15 was also not designed to operate with a carbine-length gas system, and we KNOW it causes greater wear on the bolt, right? But the design has adapted over the years. Likewise, we've see the appearance of "pads" on the read of the BCG, and "anti-tilt" buffers, not terribly unlike the addition of the H buffers, extra power extractor springs, inserts, O-rings, etc.
Still, I have yet to see any convincing evidence that it's a problem in any significant scale.
Like any design change, you'll eliminate some problems, and introduce others. Determining whether it's a net gain or net loss in reliability requires data however.
variablebinary
03-01-11, 11:59
I'm no pro or anti piston. I've owned an LWRC and LMT piston which is now DI.
My LWRC suppressed much nicer than my DI guns and was immune to even the crappiest ammo. The main reason I sold it was LWRC making so many upgrades to their system
This is why I love this forum. You guys have saved me another thousand bucks by talking me out of a piston AR.
+1!!!! Learn from the mistakes of others unless you have a boat load of money to blow.
Thomas M-4
03-01-11, 12:58
I hear ya, but I add: What failure mode are you introducing? I haven't seen any significant evidence of one. The AR-15 was also not designed to operate with a carbine-length gas system, and we KNOW it causes greater wear on the bolt, right? But the design has adapted over the years. Likewise, we've see the appearance of "pads" on the read of the BCG, and "anti-tilt" buffers, not terribly unlike the addition of the H buffers, extra power extractor springs, inserts, O-rings, etc.
Still, I have yet to see any convincing evidence that it's a problem in any significant scale.
Like any design change, you'll eliminate some problems, and introduce others. Determining whether it's a net gain or net loss in reliability requires data however.
I am not impressed with the pads on the rear of the carrier. Seths anti tilt carrier on the other hand is a better Idea.
There is another part of the problem which I think you may not realize. And I my self learned this from M4C thanks to Robb , Steven & Todd. I will try to explain it on a DI system the gas enters the carrier chamber pushing the carrier to the rear. What most fail to realize is that it is also pushing the bolt forward reducing the load on the locking lugs while they are disengaging from the barrel extension . You have none of that on a piston conversion the carrier is slapped to the rear as the carrier unlocks the bolt from the barrel extension. I believe that the [sorry if I got the name wrong] PWS system uses a spring to try to simulate this :/ I am not impressed with that solution neither. On modern designed ground up piston systems they have fewer number of locking lugs but they are bigger & beefier to handle this.
Thomas M-4
03-01-11, 12:59
Piston AR's
Add weight -
Add more parts to the system -
Slightly reduced accuracy compared to the DI system -
Add more recoil -
Both can go thousands of rounds before cleaning =
Piston AR's use proprietary parts -
Pistons are more abusive to the locking lugs that were original designed for a DI system -
Pistons may be easier to clean but you do have more parts to clean now but I will give it a + [just because that is what every piston manufacture advertises]
Sorry I don't rate being easier to clean above all the other minus's
In fact I would put it at the bottom of my list of priorities.
Not against piston designs I am just against shoe horning one in a AR-15.
Doc Safari
03-01-11, 13:00
Maybe this is a stupid idea, but why can't the piston AR manufacturers copy the Korean Daewoo K2? It seems like that's the happiest marriage of the AR receiver and AK piston system, which is what the piston AR makers are after, right?
Thomas M-4
03-01-11, 13:13
I will consent to one exception and that's HK system its still new so I still forget about it [forgive me]. If they get it to work and hold up. Ill give those Damn German engineers credit they deserve. If it doesn't and the Germans cant get it to work right I hope to god every body finally gives up on the Idea. :sarcastic:
Even the German's cannot make it work, and I love German engineering more than any other.
We've had our HK416's chew up a couple bolts. I am not impressed with them in general. I also must add that I am not a fan of piston conversions or redesigns in ARs period. They do seem to break parts more often than quality DI guns and I have not seen any advantages in terms of reliability. We run our guns hard. Mostly suppressed.
Actually, we did figure out how to fix it's problems - by putting a 9" 300 BLK DI upper on it. ;)
http://www.advanced-armament.com/st/convert.jpg
FChen17213
03-01-11, 13:38
I think the HK416 is the standard pretty much. Maybe not in the US, but around the world, the HK is the only one that is actually used by several militaries around the world. That being said, people have made some negative as well as positive comments on the platform.
Thomas M-4
03-01-11, 13:42
We've had our HK416's chew up a couple bolts. I am not impressed with them in general. I also must add that I am not a fan of piston conversions or redesigns in ARs period. They do seem to break parts more often than quality DI guns and I have not seen any advantages in terms of reliability. We run our guns hard. Mostly suppressed.
Actually, we did figure out how to fix it's problems - by putting a 9" 300 BLK DI upper on it. ;)
http://www.advanced-armament.com/st/convert.jpg
What ZEE GERMANS can't get it to work:suicide:
Robb Jensen
03-01-11, 13:49
Maybe this is a stupid idea, but why can't the piston AR manufacturers copy the Korean Daewoo K2? It seems like that's the happiest marriage of the AR receiver and AK piston system, which is what the piston AR makers are after, right?
They did the Daewoo's a bit backwards. Piston on the full size guns and DI on the small ones.
...What most fail to realize is that it is also pushing the bolt forward reducing the load on the locking lugs while they are disengaging from the barrel extension...
By the time the carrier is unlocking the bolt, the bullet has exited the muzzle, the gases have blown out of the carrier exhaust ports and the pressures have dropped to almost nothing. Even while the carrier is fully charged, the pressure inside the carrier will never be greater than inside the bore and cannot push the bolt forward.
There would be a moment that the pressure inside the carrier acts against the back thrust of the bolt, but it will be less than the pressure in the bore due to the exhaust ports in the carrier and it will be before the carrier even begins to unlock the bolt. At the point the carrier is unlocking the bolt, it has been moving from momentum alone
Thomas M-4
03-01-11, 15:29
By the time the carrier is unlocking the bolt, the bullet has exited the muzzle, the gases have blown out of the carrier exhaust ports and the pressures have dropped to almost nothing. Even while the carrier is fully charged, the pressure inside the carrier will never be greater than inside the bore and cannot push the bolt forward.
The gas system is charged almost instantly once the bullet passes the gas port.
The gas is not vented till after the bolt is unlocked from the barrel extension.
I think the HK416 is the standard pretty much. Maybe not in the US, but around the world, the HK is the only one that is actually used by several militaries around the world.
IIRC, but I could be wrong,
Turkey and Norway are the only countries that issued the 416.
other countries only got a limited number of weapons for T&E or small unites/special forces.
IMHO the 416 is still far from being the standard
The gas system is charged almost instantly once the bullet passes the gas port.
The gas is not vented till after the bolt is unlocked from the barrel extension.
Incorrect. Gases begin venting as soon as they enter the bolt carrier. Bolt carriers have vent holes. Also, the bolt carrier does not immediately begin unlocking the bolt. The carrier will move rearward a certain distance before the cam slot engages the bolt cam. Until the cam slot engages the bolt cam, the bolt remains locked. By the time the cam slot engages the bolt cam, the bullet has cleared the muzzle and pressures have dropped dramatically.
The first rule of designing a self-loading firearm for a high pressure cartridge is do not unlock the bolt until pressures have dropped to safe levels. Premature unlocking can lead to such problems as case bulging, case separation, burst cases, stuck cases and torn rims, not to mention the damage to the firearm and shooter that can be caused
Thomas M-4
03-01-11, 15:58
Incorrect. Gases begin venting as soon as they enter the bolt carrier. Bolt carriers have vent holes. Also, the bolt carrier does not immediately begin unlocking the bolt. The carrier will move rearward a certain distance before the cam slot engages the bolt cam. Until the cam slot engages the bolt cam, the bolt remains locked. By the time the cam slot engages the bolt cam, the bullet has cleared the muzzle and pressures have dropped dramatically.
How in the hell is it going to do that the bolt has gas rings [The gas can not escape until the holes on the side of the carrier are exposed] You can see the gas rings move pass the exhaust ports until that time the gas is trapped between the bolt and the carrier.
The first rule of designing a self-loading firearm for a high pressure cartridge is do not unlock the bolt until pressures have dropped to safe levels. Premature unlocking can lead to such problems as case bulging, case separation, burst cases, stuck cases and torn rims, not to mention the damage to the firearm and shooter that can be caused
That is what the cam pin slot in the bolt carrier does.
How in the hell is it going to do that the bolt has gas rings [The gas can not escape until the holes on the side of the carrier are exposed] You can see the gas rings move pass the exhaust ports until that time the gas is trapped between the bolt and the carrier.
Thank you for this correction. I do not have a BCG here (yet! I hope it arrives soon!) to look at and was working from memory
That is what the cam pin slot in the bolt carrier does.
Yes, what I called the cam slot. This delays the opening of the bolt until gases have been vented and pressures have dropped to safe levels. Venting of gases begin before opening the bolt, not after. Keep in mind venting also occurs through the muzzle & gas key
I have a 10.5" and 16" LWRC A2s in 5.56mm a few years old now and get a lot of attention. That said I have DIs as well and use them all.
The 16" is a my main training upper - eats everything - no problems whatsoever. Mucho rounds through it just via courses alone. 10.5" gets lots of suppressor and full auto play. Both have seen a good deal of full auto, but the 10.5" gets most of it.
Been very happy with both and cleaning is almost a delight(anal gun cleaning guy here thanks to Drill Sgts via basic training)
They do not have the latest piston design and solid bolt carrier(that apparently you can retrofit now) My only problem was with the 10.5"experience a sheared screw on the BC Key(thingy that replaced it) and LWRC replaced.
I have a PWS upper that started out as a conversion and has been sent back to PWS multiple times.
Issues:
Short stroking: opened up gas port
Short stroking: Pin gas block
BCG key sheared off
Op rod disassembling itself during firing due to press fit pin failure
I doubt I have ever gone more than 600 rounds before it failed. This is across several generations of their design. They have replaced everything except the upper receiver.
pointblank4445
03-01-11, 20:33
Both...guns I've seen, worked on, shot, owned, T&E'd. Some as little at 1-2K rounds on them some as much as 25K rounds.
A failure after 25,000 rounds?!? I would call that a success considering most folks who put that much ammo down range in one gun don't typically "baby" their guns. Also, I would like to know to what degree suppressor usage played in these failures....i'm sure in some cases suppressor usage was essential to the failure.
And while i'm not surprised by the general attitude toward pistons here, but the way some guys are talking, their DI guns have never gone tits up.
PB,
I don't think that anyone here said that DI guns don't fail. In fact, I know that I have said repeatedly that anything man made can fail.
The difference being that if anything fails on my AR, I can bust out the tools and fix it. Whether it be a barrel, bolt, etc.....
Most people cannot say that about a piston upper. Not to mention the fact that there is still no proof that they are more reliable.
It's also been pointed out that the average person will not recognize the value of using a piston gun.
A failure after 25,000 rounds?!? I would call that a success considering most folks who put that much ammo down range in one gun don't typically "baby" their guns. Also, I would like to know to what degree suppressor usage played in these failures....i'm sure in some cases suppressor usage was essential to the failure.
And while i'm not surprised by the general attitude toward pistons here, but the way some guys are talking, their DI guns have never gone tits up.
Heavy Metal
03-01-11, 21:05
To me, the big advantage of pistons was they didn't bake off the bolt group lube.
The new FailZero coatings mitigate this issue away to a great degree with none of the baggage the pistons induce.
Robb Jensen
03-01-11, 21:07
A failure after 25,000 rounds?!? I would call that a success considering most folks who put that much ammo down range in one gun don't typically "baby" their guns. Also, I would like to know to what degree suppressor usage played in these failures....i'm sure in some cases suppressor usage was essential to the failure.
And while i'm not surprised by the general attitude toward pistons here, but the way some guys are talking, their DI guns have never gone tits up.
Far from it. I'm very good at breaking shit left and right. This is why my new Limited gun for USPSA is a S&W M&P40 5" Pro. I got tired of dumping $100s of dollars keep my STI running.
Back to the AR. I break shit and wear shit out on DI guns on a regular basis the difference is I can get parts from Brownells, BCM, LMT, Colt, Daniel Defense, and many others and know it'll work. If I bend an op rod for piston gun it's only available from the original manufacturer same for any other proprietary parts associated with them. Also I know how to keep a DI gun running and know how to properly assemble one.
variablebinary
03-02-11, 04:22
Some people see the value of piston AR15's
http://img.photobucket.com/albums/v101/He219/mpnet/3975171034_4fc39f2415_o.jpg
http://img.photobucket.com/albums/v101/He219/mpnet/4016999104_00b4d38924_o.jpg
http://img187.imageshack.us/img187/7310/0908018a2946f046.jpg
El Pistolero
03-02-11, 04:29
^^^^^
HK416?
Allow me to chime in on that. When I was in A'stan recently (last 90 days) I was at a location where a certain Army unit that was using the 416 was located.
I spoke to some of those individuals and asked what they thought about them. All the comments were pretty positive. When I asked about maintenance, parts breakage, etc... non of them could tell me if anything was replaced.
I was told that when the return to Ft. Bragg, they get inspected and who knows what else.
I don't think that any of us are saying the 416 is bad. But, it's also not the wunderwaffe that it was touted to be. I also think that for their purposes they are probably just great. I also think that if stuff was breaking you definitely wouldn't hear them talking about it. It would more than likely come from outside sources.
Some people see the value of piston AR15's
http://img.photobucket.com/albums/v101/He219/mpnet/3975171034_4fc39f2415_o.jpg
http://img.photobucket.com/albums/v101/He219/mpnet/4016999104_00b4d38924_o.jpg
http://img187.imageshack.us/img187/7310/0908018a2946f046.jpg
I spoke to some of those individuals and asked what they thought about them. All the comments were pretty positive. When I asked about maintenance, parts breakage, etc... non of them could tell me if anything was replaced.
My friend is in unit that is oldest and most hard-use user of HK416 here. He personally is issued KAC (old version SR-16) and loves it. But guys from "front-line" use 416 and has nothing bad to say about them. They do carry them back to unit armourer but mostly to let him clean it for them or make scheduled maintenance. My friends do not remember any info on failures and problems.
They switched to 416 from SR-16 mostly because they had problem getting parts for SR-16 and found out that 416 is gives them some more margin. Before decision was made they had some samples for some time that got beaten and eventually they managed to push them to failure point. Every man made thing have failure point - it's important to know where it is.
Robb Jensen
03-02-11, 07:22
You can't really judge the quality of something because an Army 'Unit' uses it. Hell not to long ago they were using STI .40s and then Glock 22s.....
FChen17213
03-02-11, 07:34
Everything is going to break and fail at some point. They are tools. In fact, one person mentioned that if you don't run something till at least one part of it breaks, you're probably not running it hard enough. I hate it when some people find one or two guns breaking out of a whole batch after the guns have all been shot like 20,000 rounds, been abused, and went to war, and then say that the system is unreliable or a piece of crap.
That being said, I think that the pro-DI people are saying that the availability of parts of a DI gun and lack of extra weight make it a better system. They are saying that the piston guns also suffer from a few parts breakage problems and some suffer from carrier tilt. Pro piston people usually claim that the system runs cleaner in the bolt carrier area and that the guns need less maintenance in general. I think it'd be safe to say that both systems (if set up properly) have their merits.
You can't really judge the quality of something because an Army 'Unit' uses it.
I agree, and get a little tired of the "look who uses what you're poopooing" argument. My needs, budget, support, application, training, etc. are not that of a military unit. While what one uses or doesn't use, failures or successes reported, and other information may be of some value in the overall analysis, in and of itself it means little to nothing.
Robb Jensen
03-02-11, 07:59
I agree, and get a little tired of the "look who uses what you're poopooing" argument. My needs, budget, support, application, training, etc. are not that of a military unit. While what one uses or doesn't use, failures or successes reported, and other information may be of some value in the overall analysis, in and of itself it means little to nothing.
Exactly. They use lots of stuff that I don't need since my job is rocking the workbench or sales floor.
vicious_cb
03-02-11, 14:19
My friend in the Norwegian Royal Guard is convinced his 416 is an absolute piece of shit, multiple instances of broken gas regulators in his platoon, guns spontaneously turning into straight pull back rifles. Whether its ammo related remains to be seen.
http://www.dagbladet.no/2011/02/25/nyheter/innenriks/forsvaret/sikkerhetspolitikk/forsvarspolitikk/15526559/
Cincinnatus
03-02-11, 14:21
Given HK's reputation as being less than responsive to the needs of civilian shooters with it's customer servuce--in terms of obtaining replacement parts, etc. I'm glad now that I did not get an HK416.
Doc Safari
03-02-11, 14:23
Just an observation, but whenever someone cites the fact that a certain military force issues a certain firearm and uses that as a recommendation, I remember that the Chauchaut was once standard issue with a military force as well.
Cincinnatus
03-02-11, 14:24
Just an observation, but whenever someone cites the fact that a certain military force issues a certain firearm and uses that as a recommendation, I remember that the Chauchaut was once standard issue with a military force as well.
Good point. As was all sorts of other epic POSs, like the Reising submachinegun.
I agree, and get a little tired of the "look who uses what you're poopooing" argument. My needs, budget, support, application, training, etc. are not that of a military unit. While what one uses or doesn't use, failures or successes reported, and other information may be of some value in the overall analysis, in and of itself it means little to nothing.
Keep in mind that the unit used and still uses the HK416 to replace M4s. They would not do so if the HK416 was less reliable or less durable as the M4.
If the KK416 platform was nearly as problem plagued as some people suggest it would have been a flash in the pan.
In my own use of about 5K rounds, I have found it to be more reliable and less problem plagued than the S&W M&P9 & 45, both of which have suffered parts breakage and malfunctions in a similar or lower round count. And the M&P platform is considered a favorite of many people on this messageboard.
You lost me.
You're comparing the reliability of a 5.56 carbine to a 9mm and .45 handgun? :confused:
You lost me.
You're comparing the reliability of a 5.56 carbine to a 9mm and .45 handgun? :confused:
Not a direct comparison. I am just saying that my 416 has proven to be far less problematical than handguns that people routinely praise here.
To quote M4 Guru:
Military units with the latitude to test and choose literally any system...M4, Sig 55X, AK, WHATEVER....spent millions of dollars to determine that this was the best rifle. No lowest bidder that meets the standard, no Congressman trying to get dollars to his district, just simple performance at any cost. This gun (the 416) won. It was truly the best.
No, he's anecdotally describing comparitive initial platform malfunctions and relaibility issues as a stand-alone topic, and trying to malke it work while limiting it to individual experience and limiting THAT to within the percieved preferences of a narrow segment of the internet.
Kind of a stretch just to get to a glittering generality: that everything new has a shakedown period.
I see where the statement is going, but that's a bad argument to use on folks who can break it down to its component parts.
No, he's anecdotally describing comparitive initial platform malfunctions and relaibility issues as a stand-alone topic, and trying to malke it work while limiting it to individual experience and limiting THAT to within the percieved preferences of a narrow segment of the internet.
Well, we've had other people sharing their individual experiences with the HK416 . . .
Keep in mind that the unit used and still uses the HK416 to replace M4s. They would not do so if the HK416 was less reliable or less durable as the M4.
If the KK416 platform was nearly as problem plagued as some people suggest it would have been a flash in the pan.
In my own use of about 5K rounds, I have found it to be more reliable and less problem plagued than the S&W M&P9 & 45, both of which have suffered parts breakage and malfunctions in a similar or lower round count. And the M&P platform is considered a favorite of many people on this messageboard.
Sometimes even if something does not live up to the hype, might work or might not, the higher ups might just keep on using something to save face.
Not saying that the HK 416 is good or bad, but even if it had a less than stellar record, some would still crow about it.
Sometimes even if something does not live up to the hype, might work or might not, the higher ups might just keep on using something to save face.
Interestingly, that the last I heard the M4 would not be tested against possible replacements. I believe this relates to your point.
Sometimes even if something does not live up to the hype, might work or might not, the higher ups might just keep on using something to save face.
Ya think? You can begin looking at the current resident of 1600 Pennsylvania Ave, Washington, D.C., for a prime example. :)
Not saying that the HK 416 is good or bad, but even if it had a less than stellar record, some would still crow about it.
That is because it is an HK, the mythical company sprinkled with fairy dust. It is clear that the prevailing anti-piston attitude is ok around here with certain folks as long as you don't discuss the Hk416 and/or the MR556 version in the same breath as other manufacturer’s offerings.
Bottom line is any Stoner type rifle converted to piston operation is a bastardization of an outstanding design. I am still trying to understand why some seem insistent on crapping all over Gene's rifle.
Specific failures of piston AR's.
Well, experience is limited to the hk416
-bolt failures at 12-15K
-hand-guard tightening bolt failing
-cam pin gouging upper receiver (fairly cosmetic after you remove the scrapings)
-failure to feed a broad range of ammo. due to stupid fast cyclic rate and no "m4" feedramps
above failures, below drawbacks:
-heavier than traditional AR
-crappy recoil impulse, much worse than a traditional AR
-heat, the handguards get too hot to hold, fast. Radiating heat from the piston assembly cooks your rail system
-proprietary BS parts
-louder than a DI when suppressed
-a larger visual signature when suppressed
I will say I only shot a LMT piston for a demo. As compared to other piston AR's (HK & LWRC).
-used a regular AR bolt
-softer recoil impulse
-not the visual signature at night
-piston came out front, so no need to screw around with a BS rail system
variablebinary
03-02-11, 16:48
Sometimes even if something does not live up to the hype, might work or might not, the higher ups might just keep on using something to save face.
Not saying that the HK 416 is good or bad, but even if it had a less than stellar record, some would still crow about it.
The 416 is still something of an oddity. Many that choose it can just as easily carry a SCAR or M4, but make a choice to work the 416 instead.
If it was a bad weapon there is no way it would continue to see service with the high speed types after 5 years. If anything, it seems to be more popular because pics of the 416 in American hands was on the rare side, but now they are easy to find. I imagine this is why the 416 is not lumped into the pile of AR15 conversions, and is taken more seriously
http://i68.servimg.com/u/f68/15/28/41/94/devgru10.jpg
http://i68.servimg.com/u/f68/15/28/41/94/happyh10.jpg
Magic_Salad0892
03-02-11, 20:08
My LWRCi guns were problem free.
I got rid of them mostly due to cost. And because the cost wasn't justified.
Though I must say the 12.7'' A3 was quieter than my KAC 11'' gun. Though still had increased visual signature.
But it's not a fair comparison because of barrel length, and a different suppressor.
It also wasn't enough to matter.
I view DI guns as being superior now.
Heartbreaker
03-03-11, 02:14
The 416 is still something of an oddity. Many that choose it can just as easily carry a SCAR or M4, but make a choice to work the 416 instead.
If it was a bad weapon there is no way it would continue to see service with the high speed types after 5 years. If anything, it seems to be more popular because pics of the 416 in American hands was on the rare side, but now they are easy to find. I imagine this is why the 416 is not lumped into the pile of AR15 conversions, and is taken more seriously
Are you a member of one of these units? I'm certainly not but these pictures alone don't say that the users prefer, have good experiences with, or have chosen to use those rifles over something else. If you have a source by all means share it.
variablebinary
03-03-11, 03:54
Are you a member of one of these units? I'm certainly not but these pictures alone don't say that the users prefer, have good experiences with, or have chosen to use those rifles over something else. If you have a source by all means share it.
My source is I've yet to have anyone that carries a HK416 express anything other than mild ambivalence over it's performance.
"It's okay" is the usual response, not "Damn thing sucks, doesn't work and fell apart on me" in face to face conversations. Granted, the same is true for the M4 where typical feedback is "It never gave me a problem"
I don't have enough rounds through a 416 to make one break, but I am less than enamored with the heat, weight, or recoil.
Our 416's only problems are specifically the Hk "high reliability" magazines.
The springs seem to wear out faster than even the standard GI mags. This usually doesn't result in any FTF's but the bolt fails to lock back on an empty mag.
All that said. I would trade our 416's and LWRC 8'' PSD's tomorrow for simple LMT Mk18 uppers and Colt lowers.
Usually you get what you pay for, that's not the case with piston AR's.
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