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.