True, match-spec bolt carriers increase cycling efficiency for greater dependability and less chance of malfunction. Machined to military specs, hardened and heat treated, then hard-chrome plated for a much lower co-efficient of friction between the upper receiver and carrier. Inside surfaces of bolt recess are polished and also hard-chromed for a better gas seal and less carbon build-up. Includes hard-chromed gas key and stainless steel screws. Mfg: Smith Enterprise SPECS: Machined 8620 steel, Rc 58.