Although the original AR-15/M16-pattern rifle of the 1960s is a far cry from the modular M4 Carbine-style masterpieces of today, it was nonetheless by any standard a truly revolutionary design. With ultra-modern ergonomics, cutting-edge materials, radically unique operation and radical chambering, the AR was the wave of the future.
Over its more than four decades of continuous service with the United States military, the M16 series of service rifles has evolved into one of the most modular and adaptable weapon systems available today. With flattop upper receivers ready to accept optics, Picatinny rail forend systems and the ability to accept a wide range of modular pistol grips and stock assemblies, the contemporary AR is a model of modernity and modularity.
However, one element of the AR’s design has remained relatively untouched over these many decades—namely its direct gas impingement system (DGIS) of operation. In this system, gas is tapped off the bore from a port located forward of the handguard in the gas block/front sight assembly and driven back through a hollow tube above the barrel. This gas is directed back against a gas key attached to the top of the bolt carrier assembly that cups the end of the tube.
Frankly, this system is a point of contention for many shooters. Why? As the carrier is pushed back by this pressure and the action is cycled, excess hot gas and fouling is blasted into the action. Although this system provides shooters with a very accurate and soft-recoiling rifle, it also results in one in which super-heated fouling can cause the rifle to malfunction if the mechanism is not thoroughly cleaned on a regular basis.