The POF-USA Regulated Short-Stroke Gas Piston System is easy to understand. Rather than operating gas being injected directly into the upper receiver, it simply pushes a piston that acts on an operating rod (op-rod). The op-rod then acts on the bolt carrier, setting extraction and reloading into motion. This action type offers several significant improvements over the direct impingement method. First, POF guns run very clean because hot gases are not injected into the upper receiver. Carbon fouling in the action is virtually eliminated. Incidentally, the gun runs much cooler; further enhancing reliability and safety. Secondly (and arguably more importantly) POF has solved the timing problems that plague all AR-15’s with short gas tubes. Through precise op-rod/piston geometry and regulated gas pressure, all POF rifles and carbines are properly timed and bolt speeds (cyclic rates) are precisely controlled. This greatly enhances extraction and feeding reliability, as well as reduces wear and fatigue on critical components.