The M4 Super 90/XM1014 is a semiautomatic, gas operated, tubular magazine fed tactical shotgun. The bolt assembly is similar to that of the Benelli Montefeltro, with a bolt carrier and rotating two lug bolt that locks into a barrel extension. The shotgun's gas operation system incorporates a novel design, called Auto-Regulating Gas Operating, or "ARGO," by the developers. The ARGO system uses two gas ports and tappet type pistons that ride in short tubes beneath the gun's barrel. (See Figures 4 and 5.) The pistons impinge directly against the face of the bolt carrier to cycle the gun each time the trigger is pulled. According to the manufacturer, the system is unaffected by fouling, requires little or no maintenance and functions reliably with all types of standard shotgun ammunition from low brass target loads to three - inch (76mm) magnum rounds. We verified this claim in testing, as discussed below. The ARGO gas system is a simple design that we estimate will be extremely reliable in service, based on our brief, but detailed, evaluation and examination of the gun.
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