KAK Industry AR-15 300 Blackout/5.56mm NATO Bolt Carrier Group - Chrome Lined Phosphate Finish BCG, Unmarked. Phosphate coating and chrome lining-provides a BCG with excellent protection against wear and corrosion, making it a popular choice for those seeking reliability and longevity in their firearms. The phosphate coating provides an initial layer of protection, while the chrome lining offers additional durability and resistance to the stresses of repeated firing. Key Features: M16 Auto Profile Carrier Machined from Aircraft/ Bearing Quality 8620 Steel, Properly Heat Treated, Ground to Perfection, chrome lined phosphate finish; Bolt is machined from a single piece aircraft/bearing quality 9310 steel, heat treated properly, precision ground, Shot Peened and MPI'd, phosphate finsh Firing pin is machined to the mil-spec print from 8740, precision ground, and chrome plated; One Piece Billet Fully Machined Extractor, Phosphate coated for Increased reliability and corrosion resistance; Phosphate Cam Pin; S7 tool steel ejector and extractor retaining pin; 4130 Gas Key, chrome lined phosphate, precision staked using our hydraulic staking machine, Chrome lined phosphate; KAK Carrier Key Screws- T25 drive, Grade 8, Properly Heat Treated;