Abstract: Provided is a handguard attachment mechanism for use with a firearm using a standard AR-pattern barrel nut having a substantially cylindrical portion with an axial length and an enlarged diameter radial flange at a forward end. The handguard includes a substantially tubular handguard with proximal and distal ends. The proximal end includes a longitudinal slot extending from the proximal end toward, but not to, the distal end. A pair of clamping lugs, one positioned on each side of the slot adjacent the proximal end, have means for adjustably drawing the clamping lugs together to narrow at least a portion of the longitudinal slot. A circumferentially incomplete barrel nut bushing is configured to fit on the barrel nut.

Abstract: A passive safety for an AR platform firearm includes a sliding or pivoting rotating safety which is normally active to prevent trigger movement as would cause the firearm to discharge, and even when any active safety on the firearm is in a “fire” position. The passive safety is deactivated when an operator grips the firearm in a normal position to engage and pivot the trigger to discharge the firearm. Alternative embodiments are disclosed.

Abstract: Disclosed is an upper receiver assembly for use with an AR15-type lower receiver. The upper receiver assembly includes a monolithic upper receiver and forearm housing. A barrel has a breech end, a muzzle end, a bore axis, and a barrel trunnion at the breech end having a lug for direct connection to the lower receiver using the pivot pin. It includes a bolt carrier assembly, having a longitudinal slot and rail engagement with the upper receiver housing on which the bolt carrier assembly slidably reciprocates, and a long-stroke gas-piston actuation system. A recoil spring assembly is housed within the monolithic upper receiver and forearm housing and extends coaxially with the longitudinal axis of the gas-piston actuation assembly. The barrel trunnion and gas block are configured for engagement with the upper receiver and forearm housing with longitudinal keyway features.

Abstract: Disclosed is an upper receiver assembly for use with an AR15-type lower receiver. The upper receiver assembly includes a monolithic upper receiver and forearm housing. A barrel has a breech end, a muzzle end, a bore axis, and a barrel trunnion at the breech end having a lug for direct connection to the lower receiver using the pivot pin. It includes a bolt carrier assembly, having a longitudinal slot and rail engagement with the upper receiver housing on which the bolt carrier assembly slidably reciprocates, and a long-stroke gas-piston actuation system. A recoil spring assembly is housed within the monolithic upper receiver and forearm housing and extends coaxially with the longitudinal axis of the gas-piston actuation assembly. The barrel trunnion and gas block are configured for engagement with the upper receiver and forearm housing with longitudinal keyway features.