초록 ▼

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

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.

대표청구항 ▼

1. An upper receiver assembly for use with an AR15-type lower receiver in which the lower receiver attaches to an upper receiver assembly by way of a forward pivot pin and a rearward takedown pin, comprising: a monolithic upper receiver and forearm housing configured for operable mating engagement w

1. An upper receiver assembly for use with an AR15-type lower receiver in which the lower receiver attaches to an upper receiver assembly by way of a forward pivot pin and a rearward takedown pin, comprising: a monolithic upper receiver and forearm housing configured for operable mating engagement with a lower receiver assembly, the upper receiver and forearm housing including a first lug for connection to the lower receiver using the takedown pin;a barrel having a breech end, a muzzle end, and a bore axis;a barrel trunnion at the breech end having a second lug for direct connection to the lower receiver using the pivot pin;a gas block positioned on the barrel;a bolt carrier assembly including a longitudinal slot and rail engagement with the upper receiver assembly on which the bolt carrier assembly slidably reciprocates;a long-stroke gas-piston actuation system having a longitudinal axis parallel to and offset from the bore axis, the gas actuation system including a gas tube extending rearwardly from the gas block and a piston extending forwardly from the bolt carrier assembly; anda recoil spring assembly housed within the monolithic upper receiver and forearm housing and extending coaxially with the longitudinal axis of the gas-piston actuation assembly,wherein the barrel trunnion is configured for engagement with the upper receiver and forearm housing with longitudinal keyway features, one of a keyway or engagement rail being on the barrel trunnion and the other on the upper receiver and forearm housing; andwherein the gas block is configured for engagement with the upper receiver and forearm housing with longitudinal keyway features, one of a keyway or engagement rail being on the gas block and the other on the upper receiver and forearm housing. 2. The upper receiver assembly of claim 1, wherein the barrel trunnion includes laterally positioned keyway features on opposite sides thereof, the gas block includes laterally positioned keyway features on opposite sides thereof and an upper keyway feature thereon. 3. The upper receiver assembly of claim 1, wherein the gas block includes a gas port to the barrel and a manually-adjustable gas control valve. 4. The upper receiver assembly of claim 3, further comprising a closable cleaning opening in the gas block opposite and in alignment with the gas port to the barrel. 5. The upper receiver assembly of claim 1, wherein the bolt carrier assembly includes a cam pin and a rotatable bolt, the bolt having a transverse cam pin opening and an extractor and ejector positioned laterally substantially opposite each other, the cam pin opening having a axis substantially perpendicular to the transverse lateral positions of the extractor and ejector, whereby the bolt can be reversed for left or right ejection. 6. The upper receiver assembly of claim 1, further comprising a removable lower forearm cover, wherein the barrel trunnion is longitudinally held in engagement with the keyway features of the upper receiver and forearm housing by assembly of the lower forearm cover. 7. The upper receiver assembly of claim 6, wherein the lower forearm cover is removably attached to the upper receiver and forearm housing with threaded fasteners. 8. The upper receiver assembly of claim 1, wherein the recoil spring assembly comprises coil spring with a guide rod axially supported therein, the bolt carrier assembly compressing the coil spring when cycled rearwardly and the coil spring having a first stage portion and a second stage portion in axial alignment with a blocking member positioned intermediate of the first stage and second stage portions, the guide rod having a length selected such that, at a preselected point of the bolt carrier assembly's rearward cycle, an end portion of the guide rod will contact the blocking member preventing further compression of the first stage portion and limiting further compression to the second stage portion. 9. The upper receiver assembly of claim 8, wherein the second stage portion of the coil spring is stiffer than the first stage portion. 10. The upper receiver assembly of claim 1, wherein the recoil spring assembly comprises a two-part, separably engageable recoil block, a first part fixed to the upper receiver and forearm housing and a second part which is fixed to a recoil spring guide rod. 11. The upper receiver assembly of claim 10, wherein the first and second parts separably engage with mating engagement surfaces which is displaceable by forward movement of the second part relative to the first part. 12. The upper receiver assembly of claim 11, further comprising a removable transverse fastener member extending through the upper receiver and forearm housing and a portion of the recoil spring assembly to prevent forward movement of the recoil block second part. 13. The upper receiver assembly of claim 1, wherein the bolt carrier assembly includes a body in which a bolt and firing pin are received, the body at a rearward end having a firing pin retention mechanism, the mechanism including a pivoting member mounted on the body, the pivoting member pivotable between a first position wherein rearward removal of the firing pin is blocked and a second position wherein the firing pin is rearwardly removable from the bolt carrier assembly. 14. The upper receiver assembly of claim 13, wherein the pivoting member is spring bias toward the first position and manually displaceable toward the second position. 15. The upper receiver assembly of claim 13, wherein the firing pin retention mechanism further comprises a transversely slidable gate member, the gate member slidable between a first position and second position wherein the gate member blocks rearward removal of the firing pin and a second position wherein the firing pin is rearwardly removable from the bolt carrier assembly, movement of the pivoting member between first and second positions causing relative movement of the gate member between first and second positions. 16. The upper receiver assembly of claim 1, further comprising a bolt having a head with a plurality of substantially equally-spaced radially-extending lugs and an extractor situated circumferentially between two adjacent lugs. 17. The upper receiver assembly of claim 1, further comprising a bolt having a head with a plurality of substantially equally-spaced radially-extending lugs of a defined height and width, the lugs having a substantially continuously curved transverse profile, curvature of outer ends of the lugs transitioning to a curved profile of spaces between the lugs. 18. The upper receiver assembly of claim 17, the bolt further comprising an extractor situated circumferentially between two adjacent lugs.