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Old 10-24-2009, 06:36 PM
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Exclamation Do piston AR-15s break more then gas blowback?



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I was at Shooters Station in Conroe, Texas today looking over their vast AR-15 selection. One of the rifles was the new Strum and Ruger AR-15. So I asked the sales person how he liked it, and if he had fired the rifle yet.

He said that he did not like piston AR15s - that the piston design causes the bolt to wear out faster and break faster then the classic blow back design.

The sales person went on to tell me that the piston design had been around since the 1960s. And that piston design had never caught on for a reason, and that reason was excessive wear and breakage.

This is the first I have heard of the bolt breaking problem. Can someone that has experience on this topic share their experiences and shed some light in this issue?

I would really like to have one of those new Strum & Ruger AR-15s. But I need more information on how reliable the AR15 piston system is.
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Old 10-24-2009, 06:45 PM
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Default I own a POF piston driven AR...

Here's an article that will give you an idea of what the rifle is capable of...

http://www.pof-usa.com/articles/P416Torture.pdf

Here's a link to the POF web site...

http://www.pof-usa.com/

The Ruger design is new, so I can't comment on it. I know LWRC also makes a very good piston design.
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Old 10-24-2009, 06:53 PM
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My local dealer told me the same about the sig 556 design.
Old 10-24-2009, 07:12 PM
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I suspect they are operating from the idea that the DI system has a compressive buffering action that the piston type might not have to the same degree.
I have read as much on Arfcom at least.
I can't see why there would be a difference. The same concept is in use in MANY military rifles like FNs and SKS rifles.
No one is complaining there. If there is problems it may have something to do with the lugs on the bolt which are a wear point concern with ARs anyway.
Old 10-24-2009, 07:25 PM
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Quote:
Originally Posted by kev View Post
I was at Shooters Station in Conroe, Texas today looking over their vast AR-15 selection. One of the rifles was the new Strum and Ruger AR-15. So I asked the sales person how he liked it, and if he had fired the rifle yet.

He said that he did not like piston AR15s - that the piston design causes the bolt to wear out faster and break faster then the classic blow back design.

The sales person went on to tell me that the piston design had been around since the 1960s. And that piston design had never caught on for a reason, and that reason was excessive wear and breakage.

This is the first I have heard of the bolt breaking problem. Can someone that has experience on this topic share their experiences and shed some light in this issue?

I would really like to have one of those new Strum & Ruger AR-15s. But I need more information on how reliable the AR15 piston system is.
I really don't see how a piston gas system would cause the bolt to wear quicker. It is actually the opposite. THe direct impingement system that AR's classically use cause the hot gasses to blow directly into the bolt which causes heat stresses that over time will cause a bolt failure. There are numbers out on the web but I believe it is around 10,000 rounds before the bolt needs to be checked/replaced because of this.

I think the reason why it hasn't caught on is because it makes a complex weapon more complex and adds another moving part that needs to be cleaned and maintained. Also, because of the design, the piston is rather small and not very robust. That said, it is supposed to make the ar more reliable and current numbers that are out there on piston based AR's tends to support that. Remember that this is essentially what the SIG 556 is based off of, as well as the MAsada, HK 416 and other AR replacement concepts. So actually it HAS caught on, just people are not paying attention to what the makers are putting out there. The only thing that hasn't caught on is convincing the civilian market to pay the extra money for these new systems.
Old 10-24-2009, 08:56 PM
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It seems to work well in the Korean Daewoo.
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Old 10-24-2009, 08:57 PM
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I don't have first hand experience with piston ARs but have read quite a few negative reports from others on many AR forums. I was toying with the idea of the piston for my first AR build but decided it's best to go with what we know works.

Seems the story is that direct gas impingment enters the gas key and forces the bolt carrier rearward but at the same time temporarily forces the bolt forward (toward the chamber) because of the seal made by the gas rings. This causes the bolt lugs to remain locked to the barrel extension a tiny bit longer because the cam pin doesn't pull the bolt away immediately like it would with just the force of a piston on the carrier. That's supposedly why bolts fail sooner in piston systems. Apparantly the bolt lugs and barrel extension should be beefed up in a piston system but normally standard parts are used anyway.

The other negatives I've heard are extra weight, complexity and even making it fit if it's an aftermarket addition to a DI rifle. Also the negatives GoodOlFroathyOne mentioned above.
Old 10-25-2009, 12:08 AM
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Quote:
Originally Posted by kev View Post
...The sales person went on to tell me that the piston design had been around since the 1960s. And that piston design had never caught on for a reason, and that reason was excessive wear and breakage.

This is the first I have heard of the bolt breaking problem. Can someone that has experience on this topic share their experiences and shed some light in this issue?

I would really like to have one of those new Strum & Ruger AR-15s. But I need more information on how reliable the AR15 piston system is.
I bet the salesman was talking about ArmaLite's AR-18 which did have a piston in the early 1960s. ArmaLite had blundered by selling the AR-15 to Colt just before the Air Force and Army started showing interest. In doing so they also lost the rights to DI so when scrambling to offer a competing 5.56 rifle had to also go with a gas piston. I don't think there were any serious plans by Colt to add a piston back in the '60s.

I forgot to mention there are many reports of bolt tilt stressing the bolt until premature failure in AR-15 piston systems. I wonder if it's a good idea to be one of the first to try out the Ruger, especially at its inflated price. I'd be afraid to be one of their beta testers. (Hard to say since I love Ruger and have three of them!)
Old 10-25-2009, 07:37 AM
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I think we are dealing with a couple of things here, and one of the most important is human nature. People do not like change. Sometimes even the most educated people, presented with the most logical evidence, will not change their mind once its made up.

When something new comes along, a lot of people will say "we have done it that way for 1,000 years, and its worked, so there is no reason to change?"

I see lots of reasons "why" the AR-15 piston system is superior to the gas blow back system. But almost no reasons why the blow back is superior to piston. I'am thinking in a metallurgy point of view with 16 years experience working in the welding field. And not from the "I'am an AR-15 fan" point of view.

The cooler metal runs during operation, the better.
Constant heating and cooling can cause metals to weaken.
The cleaner something is during operation, the better. You have an air filter on your car/truck for a reason.

One of the problems I see is the distance between the piston rod and the bolt. As long as the piston rod is against the bolt when it starts to move backwards, everything would be fine.

If there is any space at all between the piston and bolt, that is where a problem could come in. The impact of the piston hitting the bolt, would be like a hammer hitting another hammer. Sooner or later something is going to break.
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Old 10-25-2009, 07:43 AM
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The piston system seems to work just fine in the AK47? I don't see the Russians complaining.
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Old 10-25-2009, 07:56 AM
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Quote:
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The piston system seems to work just fine in the AK47? I don't see the Russians complaining.
The AK uses a long stroke gas piston system, the system in piston AR's is a short stroke system.
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Old 10-25-2009, 08:00 AM
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Quote:
Originally Posted by kev View Post
I think we are dealing with a couple of things here, and one of the most important is human nature. People do not like change. Sometimes even the most educated people, presented with the most logical evidence, will not change their mind once its made up.

When something new comes along, a lot of people will say "we have done it that way for 1,000 years, and its worked, so there is no reason to change?"

I see lots of reasons "why" the AR-15 piston system is superior to the gas blow back system. But almost no reasons why the blow back is superior to piston. I'am thinking in a metallurgy point of view with 16 years experience working in the welding field. And not from the "I'am an AR-15 fan" point of view.

The cooler metal runs during operation, the better.
Constant heating and cooling can cause metals to weaken.
The cleaner something is during operation, the better. You have an air filter on your car/truck for a reason.

One of the problems I see is the distance between the piston rod and the bolt. As long as the piston rod is against the bolt when it starts to move backwards, everything would be fine.

If there is any space at all between the piston and bolt, that is where a problem could come in. The impact of the piston hitting the bolt, would be like a hammer hitting another hammer. Sooner or later something is going to break.
You pretty covered the faults in the DI and short stroke piston systems. One other issue not mentioned with the short stroke AR's is that this is an after market concept and not an original design concept. So this is after-engineered which is never the best thing in the world.

That said, to clarify the cons of the direct impingement systems;
-causes fouling of the bolt face requiring more frequent and detailed cleaning
-causes premature failure of the bolt due to excessive heating and cooling
-is harder to clean
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Old 10-25-2009, 12:28 PM
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Well except for people who just buy whatever the gunshop has in stock that day, you sure can agonize over every detail of the AR you're looking for. I'm sure most of us here put a lot of thought and research into any major purchase - certainly a firearm that may be used to defend yourself and family.

It's good to get both sides of the story here and I thank you guys for bringing it up since it's something I'm concerned about too. Though I carried an M16 in Vietnam I've gotten way out of the loop until this year when I decided to back up my AK with an AR. As I got up to speed I decided to build one instead of buying off the rack. Even with a custom build there are compromises and a biggie for me was direct gas impingment over a piston, mainly just as Kev said - it's been done that way so long I didn't want to go against "milspec" when I know it works if you keep the AR clean and lubed.

For my M4 build I did go with a midlength gas system instead of carbine length to soften the beating the bolt and carrier take. That and proper maintenance and good ammo/mags should keep the rifle reliable.

Anyway, I'd certainly be interested in how the Ruger works out. Sure hope it works great. No doubt it's a little scary with any new design but Ruger rarely puts out a bad gun and if they do they work with you to get it right.
Old 10-25-2009, 12:41 PM
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Quote:
Originally Posted by GoodOlFroathyOne View Post
The AK uses a long stroke gas piston system, the system in piston AR's is a short stroke system.
Most retrofit systems are short stroke I believe. Bushmaster might be long stroke. Short stroke is harder on the gun.

Carrier tilt is a problem they don't tell you about when buying a drop in piston system. I just installed a anti-tilt buffer in my Colt Car which was showing EXTREME wear in the buffer tube from carrier tilt. This happened in less than 100 rounds.

Here is a link to the carrier tilt issue and the fix for retrofitted systems.
http://www.ar15armory.com/forums/Ant...lt-t39548.html

I'm heading to the range early next week and putting at least a couple of hundred rounds through the AR to check reliability and wear on the tube.

All this said I'd be a lot more concerned with reliability of a retrofit system than one designed from the ground up like Ruger. Ruger is known for OVER engineering their revolvers. They probably did the same with the AR.
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Old 10-25-2009, 12:52 PM
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Ah, finally some real world experience, SurvivalCop! I mistakenly called it bolt tilt but you're absolutely right the problem really is carrier tilt and the galling that results from it. Hope you've got the problem worked out now.
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Old 10-25-2009, 06:15 PM
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the only difference i noticed is that the piston adds some more kick to the gun. its just one more metalic piece flying backwards adding to the recoil.
Old 10-25-2009, 06:41 PM
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if your gonna buy a ar-15. Buy a Rock River Arms. I own 2 and they work great. Dea put in a order last year for a couple thousand after testing them.
Old 10-25-2009, 06:52 PM
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Quote:
Originally Posted by SurvivalCop View Post
Most retrofit systems are short stroke I believe. Bushmaster might be long stroke. Short stroke is harder on the gun.
All piston AR's are short stroke, if it were long stroke the piston would be attached to the bolt carrier.

The long stroke is derived from some machinegun systems. It is know for more reliability under high rates of fire and continuous fire and is resistance to fouling affecting the gas system. The m-240 machinegun uses this same type of gas system. Direct impingement is meant to increase reliability, which it does to a certain extent minus the decreased life of the bolt.

I agree the retrofit piston systems are a problem. I would hope that the companies making piston based ar's, like Ruger, have done their homework and alleviated any compatibility issues.
Old 10-26-2009, 12:10 AM
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A retrofit kit can be problematic because the gun's design just isn't made for gas piston action. Some of the better kits work better, but cost more. But a gun designed from the start to be piston driven isn't going to be an issue. I have a lot of interest in Ruger's gun for that very reason. That and their reputation for building guns like a tank.

The thing to consider when seeing a concensus on forums is that most of the people that hate the gas piston guns are most likely to be the ones who don't use it. Discard those and look only for opinions from gas piston gun owners. That'll give a more realistic view of the real experience with them. I haven't shot enough of them, to have a valid opinion. They all worked fine, but then again, I didn't put 20,000 rounds through any of them.
Old 10-26-2009, 01:37 AM
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Quote:
Originally Posted by GoodOlFroathyOne View Post
All piston AR's are short stroke, if it were long stroke the piston would be attached to the bolt carrier.
If you say so.

PWS Diablo Long-Stroke Gas Piston/Op-Rod-Driven 5.56mm AR-15 SBR Upper
http://www.defensereview.com/pws-dia...-15-sbr-upper/
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