Based on the M4 military shotgun used by the U.S. Marine Corps, the Benelli R1 Endurance Semi-Auto Rifle boasts a trim profile with fast handling and classic good looks. Auto-regulating, gas-operated (A.R.G.O.) system features a gas cylinder positioned for a short operating rod, resulting in less felt recoil. BE.S.T. treated piston rod offers superior reliability. Free-floating, cryogenically treated barrel has been mated to a sturdy steel receiver to ensure outstanding accuracy. Drilled and tapped for optics. Includes user-adjustable shim kit. Based on the M4 military shotgun used by the U.S. Marine Corps Auto-regulating, gas-operated (A.R.G.O.) system Gas cylinder position for a short operating rod BE.S.T. treated piston rod for superior reliability Free-floating, cryogenically treated barrel Sturdy steel receiver and a lightweight aluminum lower receiver Drilled and tapped for scopes Includes user-adjustable shim kit