There’s a debate raging in the AR15 community. The point of contention: operating systems. Traditionalists favor direct impingement. Designed by Eugene Stoner, DI harnesses the power of the gasses trapped in the barrel to cycle the rifle’s action. It’s a remarkably simple system with one critical flaw: the gasses blow directly into the rifle’s upper receiver and bolt carrier. Over time, this leads to a dirty rifle. In a gas piston system the propellant gases push a solid rod that pushes the carrier to the rear. That makes for a cleaner running gun. While the controversy continues, SIG SAUER has covered its bets with their piston-driven 516 and, now, the 716 . . .