So, I have chosen to use Gun Digest as my gun publication of choice and I will be arguing the point that piston driven firearms are better than direct gas impingement. While the article does list facts in favor of both types of firearms the first two examples, they list are in favor of the gas piston operation. First, they say “Piston-driven guns run much cleaner” and I can agree with this statement. Most of the carbon buildup happens in the tube that the piston sits in and never reaches the action or bolt assembly making it run more reliably. A number of militaries around the world run piston driven firearms for this reason. When you need your machine gun to run and your life depends on it, this seems like the right choice.
Second, they say “Piston-driven guns run much cooler” and again I will have to agree with them on this. If firing a few rounds at a time with both types of firearms, you may not realize a difference but with a sustained rate of fire the difference is noticeable. Also, speaking from experience I have seen the direct gas impingement of the AR platform fail when running full auto for too long. The gas tube can get to a glowing red-hot state and on rare occasions the tube splits and out gases instead of directing the gas needed to continue cycling the bolt. Granted this was during a torture test but to prove this I ran four 30 round magazines through a full auto M-16 and was able to light my cigarette off the gas tube. Seems a little too hot and unreliable to me.
Resources
Mann, Richard A. “6 Facts about AR-15 Direct Impingement vs. Gas Piston.” Gun Digest, 21 May 2020, https://gundigest.com/gun-reviews/rifles-reviews/ar-15-gas-impingement-vs-piston.
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