Benelli M4 Tactical Pistol Grip Stock 12 Gauge 18.5" 6 Round, FDE - Limited Edition When the U.S. Marine Corps went shopping for a shotgun, they bought the M4 - the 12-gauge shotgun that functions the first time, every time. Its unique Auto Regulating Gas Operated (A.R.G.O.) system developed by Benelli engineers has dual stainless steel, self-cleaning pistons located just ahead of the chamber that operate directly against the bolt assembly. The M4 Tactical comes standard with a Picatinny rail for optics, a fully adjustable ghost-ring rear sight and fixed-blade front sight and a black synthetic pistol-grip style stock. An optional standard stock is offered. With features and reliability that do it for the U.S. military, the Benelli M4 is an excellent choice for your own home defense plan. Auto Regulating Gas Operated(ARGO)