M16 Auto Profile Carrier Machined from Aircraft/ Bearing Quality 8620 Steel, Properly Heat Treated, Ground to Perfection, BlackNitride Finish by H&MBolt is machined from a single piece aircraft/bearing quality 9310 steel, heat treated properly, precision ground, Shot Peened and MPI'dFiring pin is machined to the mil-spec print from 8740, precision ground, and chrome platedOne Piece Billet Fully Machined Enhanced Extractor, Phosphate coated for Increased reliability and corrosion resistanceNitride Cam PinS7 tool steel ejector and extractor retaining pin4130 Gas Key, nitride, precision staked using our hydraulic staking machineKAK Carrier Key Screws- T25 drive, Grade 8, Properly Heat Treated