Question about piston AR's

[DanThaMan]

I like the looks of the Ruger sr556, sig 556 classic, and the barrett rec-7. I don't have the funds to buy one anytime soon, but If i ever do decide to get one in the future, I'd like to learn more about them. I have heard of something called "tilt" with piston AR's... what exactly is this?? I think it has something to do with the magazine.

Also, (this might be waaay off) I recall reading about a custom feature one could equip on their piston AR and it would negate the "tilt" action.... some anti-tilt mechanism. Is there such a thing? How does it work, and how much does it cost?

On a side note, I don't have a problem with my RRA DI system AR, I just want a Piston AR for it's reliability (don't care about 2 or 3 MAO difference). This would be a "combat/ HD" rifle if I ever get one, and I don't see the issue with lost accuracy when the effective range of the .223 is about 300-400 meters anyway.

[jeo556]

The "tilt" that you refer to is the fact that the original AR-15's bolt carrier was not designed to have railways. The carrier just fits into the upper reciever. And because the original design is a direct gas impingment, the forces that drive the bolt rearward act on the same centerline as the bolt causing it to move straight back.

On a piston driven AR, the force (piston acting on the top of the carrier) to operate the bolt is off-center from the bolt carrier centerline and causes a eccentric force, or "tilt", of the bolt. Other piston driven guns usually have bolt railways that eleviate the tendency of the bolt to "tilt". AK's for instance, have rails that the bolt & carrier ride on.
In other words, the off-center recoil force puts a small amount of torque on the bolt carrier which causes it to want to "tilt".

After inspecting the interior of my upper reciever, I'm not totally sold that the small amount of allowable movement could cause any harm but I couldn't say for sure.

If you wanted to eliminate this "tilt" I think that you would need to someway alter the bolt carrier and the interior of the upper reciever.

[Bartholomew Roberts]

Jeo556 described the issue well. Because an AR15 receiver did not need rails, it wasn't designed with them so the bolt carrier tilts when you push it from the top.

Typically, this is fixed by adding material to the bolt carrier so it cannot tilt (make circumference fatter, add "skis", etc.). However you have to question how reducing the space between the upper receiver and the bolt carrier even more contributes to reliability - especially in regard to fine sand or other debris.

Most of the more successful designs seem to just do their best to design around it and accept some amount of tilt-related wear under the theory that the tilt-related wear is less of a problem than what they are trying to correct with the piston.

If reliability is your main concern, I would shop very carefully. Not all piston systems are built equally and at least some of them are less reliable than the DI system they are replacing.

[GONIF]

AR's do not need a piston,they work just fine as DI. try a Colt 6920 or a LMT with Quality ammo and just try and make it malfunction or wear out . the piston is a solution in search of a problem a Quality AR does not have .

[davlandrum]

+1 GONIF

Sorry, I just don't see the "problem" that the piston "fixes". Especially if you told me I had to trade

2 or 3 MAO difference

for a perception of better "reliability".

Luckily, this is still the land of the free, so buy what makes you happy.

[DBAR]

Check into CMMG. They've done a lot of research with anti tilt bolt carriers, and I've seen their "Military/LEO" version. It looks pretty tough, and they have tested 10's of thousands of rounds through it. Search YouTube for some of CMMG videos. There are a few pretty cool ones of them doing 100rnd mag dumps, one after another with their Gas piston system. One handed at that.

With that being said....

I like my direct impingment AR15's just fine. Someday when I have some extra money laying around, I'll pick up one of those fancy piston jobbies.

DBAR

PS
I do wish I had the money to pick up a nice one though....

[Brenden]

I too see no problems with the DI guns,especially the Colt's..

But would love to play with the piston gun and a tub-o-ammo!!!

[TheRifleman]

AR Pistons = solution looking for a problem.

Stick with DI on the AR platform, the design is darn near perfect.

[blhseawa]

IMO, which is just as valid as any other, and not meaning any disrespect, but the comments to this thread's question, are just plain off base.

Whatever it is you'll are smoking , could you should share it!

The question is not whether the AR15 platform is reliable or not, or whether the it does or does not need to be Piston/Op-Rod or not (period).

The real question is what configuration is the AR15 and what problem are you trying to solve, in what environment?

My advice when it comes to things mechanical, do what Missourians' do, and ask them to show it to you, and then prove it to you!

I have news flash, the M4 and M4A1 have serious reliability issues in high dust environments like Afghanistan and Iraq, especially when operated in full-auto mode! Just read the after action reports!

When they "created" the carbine version of the AR15 platform and shortened the barrel and moved the gas port approximately 7 inches from the chamber, they created an engineering nightmare! They still have not resolved all of the issues they created!

Without creating another testing methodology debate, in high dust environments the average failure rate is 1 in 5000 rounds. Whether operated in full-auto or semi-auto and what type and manufacturer of magazine also plays a role. None the less, both Direct Impingement (D/I) and Piston/Op-Rod mechanisms had similar failures rates.

There are some Piston/Op-Rod based short barreled AR15 carbines that have tested to 1 in 20,000 failure rate, but currently this design is very expensive to manufacture/buy.

I said my piece, and in closing on the Nothwestern Shores of the Great Northwest my 20" D/I AR15 has never experienced a failure at the range or in the field.

YMMV

[Bartholomew Roberts]

Without creating another testing methodology debate, in high dust environments the average failure rate is 1 in 5000 rounds.

Failure rate or stoppage rate? And what was the source of that number? I ask because the Swedes claim a 3,200 MRBS for their AK5, which is basically a 5.56mm AK and has the reliability typical of that design.

[GONIF]

Quality AR,Quality Ammo,lube it right (wet) and there is no problem with the DI AR/M16/M4 .

[brmfan]

As with most comparisons, I would say "it depends". Under normal use (range, plinking, field etc) I see no clear advantage to either system. Under non normal use such as dumping a Beta C mag one after another, then the piston has an advantage (seen torture tests where gas tubes literally melt) but how many times does anyone even come close to being in such a situation!? I would bet almost never. The only real difference I have seen, having owned both, is the internals on the piston gun stay MUCH cleaner, but even then you'd need to chew through 100+ rounds to notice the difference.