Cameron Hopkins, from the American Rifleman, talks to both sides of the gas impingement vs piston operation systems for the AR platform of rifles. I have a barebones M4 style AR-15 rifle. I’ve heard both sides of the debate, and like Cameron I run a gas impingement system rather than piston.
A friend that shoots competitively for the CMP and NRA with AR-15 rifles also prefers the gas impingement system as well. He witnessed a torture test on a standard gas impingement system AR-15, to see how long it could go without cleaning. Approximately 100 rounds were fired each week through the AR-15, and it wasn’t until 6,200 rounds later that there was a single failure (fire, feed, extract, eject).
I know that the piston system is supposed to prevent the AR platform of rifles from ‘pooping where they eat’ but with the results of the torture test, I’m in no rush to convert my AR-15 over to a piston system. Not to mention that Hopkins mentions a bit about pistons causing the bolt carrier to tilt slightly — which was never designed to be tilted — thus possibly causing problems down the road.