Provided is a firearm lower receiver configured to mate with an AR-pattern, auto-loading upper receiver assembly. The lower receiver has a body and a hinge mechanism having a fixed part integral to the lower receiver body and a moving part to which a buffer tube is mounted. The hinge is movable between an extended, operating position where the buffer tube is substantially aligned with the bolt carrier and a folded position. The fixed part includes a carrier blocking member movable between a blocking position where the blocking member prevents rearward movement of a bolt carrier in the upper receiver and a displaced position. The blocking member is spring biased toward the blocking position. A striker extends from the moving part and is configured to contact the carrier blocking member and move it against the spring bias to the displaced position when the hinge mechanism is in the extended, operating position.