Chambered in 5.56 mm NATO (.223 Remington) and use the battle-proven Auto Regulating Gas Operated (ARGO) system—the same system developed by Benelli for the M1014 (M4) and used for over a decade in multiple conflicts by the United States Marine Corps Built to the same tough military specifications and embodying the solid reliability that the U.S. Marines rely upon Stainless steel, self-cleaning piston that operates directly against the proven rotating bolt Piston-driven system - incorporates a gas port located just forward of the chamber, where the gases are hotter and cleaner, resulting in less fouling and more reliable cycling O.A.L.: 37.1” Barrel: 20” Avg. Wt.: 7.9 lbs.