Have you ever wondered what the impact of using Gas Direct Impingement or a Piston system on your AR15?  First of all, AR15's are not "100% True Direct Impingement" because the gas doesn't push the bolt carrier group directly rearward, it puts gas into the "bolt" area of the carrier group and pushes the "bolt" directly in line with the barrel.  This is why AR15's have a recoil impulse directly rearwards.   So lets just call it "BCG Gas Driven" since gases are hitting the bolt carrier group, period, end of story, versus Piston, which sits up front, and ejects the gases forward toward the muzzle.  This is why Piston setups run far cleaner.  Far is not justice.  I would say multitudes cleaner, like a different planet of cleaner.    So lets see if Piston VS traditional Eugene Stoner AR15 design affects accuracy at all.  That is all we care about here.  Which system is more reliable?  Well, the military just switched to Piston, and the world has been using piston for, a long, long time, such as AK47.  You name it.

So let me settle this debate.  A "Piston/Rod" system does not "start" the movement of the bolt carrier group, gas does.  End of story, done, ding ding ding, winner.  I like piston better overall, honestly.  I like how clean and free moving the BCG is with it. 

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Piston VS Gas Tube
Compass lake Engineering, Douglas Barrel.

The target on the left is PISTON system, which has a steel rod in place of the gas tube.  When you fire a shot, the gas from the barrel, goes into the gas block and pushes the steel rod backwards, directly against the top of the bolt carrier group.  The gas then blows out the front of the gas block, forwards and away from the shooter.  

But we wear glasses, so who cares about that, which system is more accurate.

The Traditional Eugene Stoner Gas driven gun, using standard gas tube, is more accurate.  But why?

Well, there could be a few reasons to consider.  Primarily, for the same reason you want free floating hand-guard that is not touching the barrel, is perhaps a sufficient argument.  When you shoot a piston gun, you have a "loose" heavy, steel rod that moves, and its attached to the barrel.  That can't be good for accuracy. 

Another argument is that a piston system does not push the BCG back directly in line with the barrel, it pushes the TOP of the BCG back, thus causing BCG tilt, and causing recoil impulse to not be directly rearward, but slightly up and down too. 

BAck to the target.   Gas system is more consistent, less propensity for flyers, and tighter groups due to more stable platform.  Those are 7 round groups.  Statistics below
Another gun
White Oak Armament Shilen 20"
Again, we see improvement to consistency, with smaller flyers using the gas version.  This was 6, totally different loads, and the load on bottom right, was 10 shots each.  See how the piston had 3/10 flyers and the group with gas had 0 flyers and is just 1 nice sub MOA group? The group on upper left is another good example.  1 tiny flyer on Gas version, and the piston version was erratic.

Numbers don't lie
In both guns, you have same trend.  And with both guns  the best groups were with the gas setup.  Notice the WOA setup had 4 of the top 5 scores with Gas, and the CLE barrel 3/4 best groups were with the Gas?

Gas is more accurate folks.  Thats it.  How much more accurate is it?  If we could ever shot, its basically .3-.4 MOA better.  If we could best 6/7 shots its marginally better, and if we count the best 5 shots its basically .1 MOA better (round up).

You see how consistent the results were gun to gun?

Bottom line...Gas system has less flyers, and when they do, they are less impact.  This is the conclusion.
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