the pressure regulator being non adjustable in the case of a non adjustable pressure regulator the size of the orifice 58 b will be determined based on a compromise for intended and predicted conditions as depicted in fig6 a and 6b displacement of the operating rod 64 from the static position s to the displaced position d results in a corresponding displacement of the yoke 47 a the tappet rod 47 b is engaged with a bolt carrier lug 36 a of the bolt carrier 36 the bolt carrier lug 36 a is constrained to forward and rearward movement in a bolt carrier lug channel 42 b fig7 of the upper receiver body 42 accordingly the displacement of the operating rod 64 also results in a corresponding displacement of the bolt carrier 36 the displacement of the bolt carrier 36 that is associated with the displacement of the operating rod 64 is an initial displacement of the bolt carrier 36 due to inertia associated with the speed at which the operating rod 64 is displaced the bolt carrier 36 continues to travel after the operating rod 64 reached its maximum displacement thus the overall displacement of the bolt carrier 36 is greater than the displacement of the operating rod 64 accordingly the upper receiver assembly is said to be gas energized and piston driven implementation of embodiments of the.