Army Testing Shows Piston Retrofit kits Are Not Less Accurate, And. . .

[lysander]

One curiousity is the accuracy.

Baseline with the ARS handguards ranged between 2.5-4.5"

Replacing the ARS handguards with plastic and installing the piston kits ranged between 2.5-3.5", with most around 2.5".

Perhaps the handguards rather than the piston are main the source of the accuracy improvement.

What other possible explanation is there for the accuracy improvement?

O1 - .567" improvement
O2 - .760" improvement
A1 - .700" improvement
A2 - .755" improvement
C1 - 1.373" improvement
C2 - .494" improvement
B1 - .574" improvement
B2 - .945" degrade

Average ES baseline (DI) - 3.300"
Average ES piston - 2.641"

20% improvement, that is statistically significant, indicating something improved the accuracy in general.

[lysander]

Going over the report again, the actual model is given, and it is one the the more popular models out there. This model suppressor uses a proprietary flash hider/mount that was required to installed on the barrel threads in lieu of the standard flash hider and the suppressor engages the proprietary flash hider/mount. During the testing, the flash hider/mount became loose, due to breakdown of the thread locker. The suppressor remained firmly attached to the flash hider/mount.

They used the supplied material, and followed the manufacturer's instructions. Reading the list of stuff supplied in the kit for the suppressor flash hider/mount installation (published by the manufacturer and found on-line), Rocksett thread locker is what was supplied.

And yes, that model is issued and yes, they (ARDEC) are looking into corrective action to prevent this from being a problem in the field.

[JC5188]

O1 - .567" improvement
O2 - .760" improvement
A1 - .700" improvement
A2 - .755" improvement
C1 - 1.373" improvement
C2 - .494" improvement
B1 - .574" improvement
B2 - .945" degrade

Average ES baseline (DI) - 3.300"
Average ES piston - 2.641"

20% improvement, that is statistically significant, indicating something improved the accuracy in general.

I find this the most interesting. I'd always heard the opposite when talking about short stroke Pistons. Anecdotally, I'd never experienced it with my piston rifle vs my DI rifles, although I'd never conducted a scientific test either.

For my purposes, which is pretty much shooting steel 0-300m, I've found no practical difference. It's great to see actual test results.

Thanks for this info.


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[Clint]

All of the problems seem to stem from the higher cyclic rate, and a high cyclic rate can be controlled by heavier buffers smaller gas ports and sometimes choice of springs.

Totally agree.

To be more fair to the piston kits, they could be "re-baselined" with more normal cyclic rates using buffer weights or gas port adjustments.

[lysander]

Totally agree.

To be more fair to the piston kits, they could be "re-baselined" with more normal cyclic rates using buffer weights or gas port adjustments.

This is the reason the argument will never be resolved.

The anti piston crowd will say:
"The kits are sold as kits, theoretically everything you need to go from "DI" to "piston", therefore if the cyclic rate needs to be dropped, a heavier buffer should be included."

The pro-piston crowd will counter:
"Over-gassing in "DI" ARs is a common cause of malfunctions, since so many ARs out there are not to "spec" in regards to port size, carrier weight, spring stiffness, etc, etc."

On the other hand, one might say, the various manufacturer's could use this information to tweak their designs so the cyclic rate doesn't increase so much.

And therein lies the problem for the poor piston kit manufacturers, with so many non-spec gas ports, and carrier/buffer combinations what do they design to? They kind'a have to make it work reasonable well for the least gas condition, which hurts the mximum gas condition, but in both conditions, it works out of the box, which is what the customer demands.

I have an idea for the next big thing in AR build tools, a timer that can measure cyclic rate without having to go full-auto. That way you can tailor weights and springs to keep the cyclic rate between 700 and 970 (the specified rate for a new barrel with an un-eroded gas port) or below 1025 maximum (spec rate max after after 6000 rounds).

[cd228]

What's the DTIC document number? I'd like to download a copy for my files.

[lysander]

What's the DTIC document number? I'd like to download a copy for my files.

The Accession Number is ADB400492.

However, it should be noted that this document has Distribution Statement B, so it is not accessible through the public DTIC website.

[cd228]

The Accession Number is ADB400492.

However, it should be noted that this document has Distribution Statement B, so it is not accessible through the public DTIC website.

Thank You.

[Noodles]

lol at you some of you guys cherry picking just the accuracy numbers out

4 of 8 of the Pistons didn't even finish the test, the ones that did all had higher failures than the DI... But cook off and wear on the bolt were lower both nearly inconsequential for civilian users who these kits are targeted at.

It can more fuel to the fire for some, but all I see is that Piston-Mania 2009 was stupid and DI rifles really are great.

[SomeOtherGuy]

It can more fuel to the fire for some, but all I see is that Piston-Mania 2009 was stupid and DI rifles really are great.

I've bought and sold a popular brand of piston upper twice now, each time thinking it would be cool and more reliable than my already 99.9% reliable DI uppers. Each time I discovered it's awfully front heavy (two different versions), the dirt and crud not inside the receiver is simply splattered around the gas block, barrel and handguards, recoil is sharp, and while they each worked fine, there was no obvious benefit for going to something proprietary. This second time I tried to be very thorough in getting it tuned, and discovered that it really needed an H3 buffer to work at a reasonable pace. H2, H, A5, and rifle buffer setups all produced excessively fast operation. I tried it with the gas setting on the suppressor position and got only short-stroking and failures. H3 was about right but a bit sluggish, while H2 was still obviously over gassed. I also had plenty of tiny brass flakes and shavings and obvious damage to case rims when using H2 or lighter buffers (though not with the H3). That brand, which is among the best regarded, is IMHO a solution in search of a problem, and the creator of new problems.

Tieing this with the thread, excessive cyclic rate was an issue with the various piston kits tested, and an issue with the two I've had.