Gas Piston AR: less accurate than direct impingement?


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6.5x39
July 14, 2009, 02:03 PM
I recall seeing a slow-motion video on YouTube of an AK-47 being fired in automatic mode, and the barrel was bouncing up and down based on the bulk of the gas piston slamming against the back of the receiver and the slamming closed again (before starting all over again). I've frequently seen articles and essays about how much cleaner and cooler the bolt in a gas piston AR is, but I've never see any comment on whether the mechanics of the gas piston affect the accuracy of the rifle. Does anyone know if a gas piston affects the accuracy of an AR?

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Dr. Tad Hussein Winslow
July 14, 2009, 02:17 PM
I don't know about the other GP guns, but the HK 416 will likely shoot 0.00000001 MOA, in keeping with its magical powers that allow it to shoot unaffected with a bore obstruction.

Sorry that probably doesn't help much. :)

everallm
July 14, 2009, 02:34 PM
A large chunk of why the AR platform can be highly accurate has very little to do with the miracles of DI and far more due to the tight tolerances of the AR.

These tight tolerances are one of the contributory factors for the need to keep the AR platform cleaner for equivalent reliability than some piston platforms.

(Waits for the followers of the Holy Church of AR to start flaming 'cause they didn't read the words "one of the" and "some".......:evil: )

nyresq
July 14, 2009, 05:26 PM
For accuracy consider that in semi auto, the projectile will be out of the bore and on its way before the piston slams into the carrier or back into the gas block. And since all that happens in a fraction of a second, the bolt will be home, trigger will be reset and the piston will no longer be in motion before you pull the trigger again.

And if you are talking about full auto fire, then accuracy isn't going to matter if its .5moa or 5moa...

Owen
July 14, 2009, 06:06 PM
I can say for a fact that the HK 416 offers less than stellar accuracy.

praharin
July 14, 2009, 07:06 PM
A large chunk of why the AR platform can be highly accurate has very little to do with the miracles of DI and far more due to the tight tolerances CLEARANCES of the AR.

These tight tolerances CLEARANCESare one of the contributory factors for the need to keep the AR platform cleaner for equivalent reliability than some piston platforms.

(Waits for the followers of the Holy Church of AR to start flaming 'cause they didn't read the words "one of the" and "some"....... )

Fixed that for you, look up the definitions of those words, in terms of engineering. You'll see.

To my understanding, the reason that DI CAN be more accurate that a piston rifle is because it doesn't have the added movement/friction of the piston interfering with the way the bolt closes. The added weight has nothing to do with it because weight does not effect mechanical/potential accuracy.

HorseSoldier
July 14, 2009, 07:25 PM
I can say for a fact that the HK 416 offers less than stellar accuracy.

+1

The ones I have personal experience with were 4-5 MOA guns with green tip.

RP88
July 14, 2009, 07:42 PM
with DI, all of the movement and friction is in-line with the entire gun. That is the big factor there: balance.

SlamFire1
July 14, 2009, 08:34 PM
I believe a large contributor to the outstanding accuracy of the AR is the lack of an operating rod.

The less parts, the fewer things to vibrate.

I also believe locking lug symmetry helps.

I don't like DI for a combat rifle, as fouling needs to be kept out of the mechanism, but for a target rifle, the .223 AR's and the 308 versions are exceptionally accurate.

Darthbauer
July 14, 2009, 08:39 PM
The LWRC that I have shot felt far more accurate/less recoil than my DI AR.

everallm
July 14, 2009, 08:51 PM
Praharin

Thank you for your unsolicited help, I am more than aware of the differences and used the wording deliberately as it is in general common usage and understood by the reader in general.

briansmithwins
July 14, 2009, 09:01 PM
I believe a large contributor to the outstanding accuracy of the AR is the lack of an operating rod.

The less parts, the fewer things to vibrate.

I also believe locking lug symmetry helps.

I don't like DI for a combat rifle, as fouling needs to be kept out of the mechanism, but for a target rifle, the .223 AR's and the 308 versions are exceptionally accurate.

Interesting. I thought the Garand and M1A were the best targets rifles...

BSW

nad1967
July 14, 2009, 09:05 PM
I shot green tip with my PWS and shot around 3 MOA... switched to Federal bulk and shot consistent 1 MOA

all at 100yds

SHvar
July 15, 2009, 12:48 AM
Theres an increase in percieved recoil in GP ARs, this takes getting used to but the round is out of the barrel and gone before the movement of the piston affects the rifle.
Compared to a DI AR the GP model seems to be harder to hold still mainly if firing rapid. In fact its obvious in the feel produced by firing GP rifles standing and on a rest. Where as the DI model feels less recoil when fired from a rest, the GP model feels as if there is increased recoil while fired on a rest. While standing/or unsupported there is little to no difference between them.
This can translate into less accuracy in comparison, but like any difference in design or function the differences can be adapted to by the way the shooter operates the weapon.
I see these differences as a small trade off for much decreased maintance, much decreased heat, wear, almost no carbon in the upper reciever at all, much reduced need for lubrication, and absolutely no fouling of the recievers and moving parts.
Both have advantages, and disadvantages, I like both personally.

jpwilly
July 15, 2009, 01:53 AM
The AR has gotten more accurate for the same reasons the new breed of hunting rifles are more accurate than ever.

Free floated barrel
The lockup of the bolt is consistant
Triggers have gotten a lot better.

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