KAK Industry's durable and dependable 5.56 NATO bolt carrier group features a chrome lined interior and phosphate finish. As the workhorse of our BCG lineup, it is built to deliver years of reliable performance without the high-price tag. M16 auto profile carrier machined from aircraft and bearing quality 8620 steel, properly heat-treated, precision ground and finished with a heavy chrome for durability and performance Bolt machined from a 1-piece of aircraft and bearing quality 9310 steel, properly heat-treated, precision ground, shot-peened and MPI tested for reliability and durability Firing pin machined to Mil-Spec print from 8740 steel, precision ground and chrome-plated for durability and corrosion-resistance 1-piece billet, fully machined enhanced extractor with a phosphate coating for increased reliability and corrosion-resistance Chrome-plated cam pin S7 tool steel ejector and extractor retaining pin for enhanced strength and durability 4130 steel gas key, fully chromed and precision staked using a hydraulic staking machine KAK carrier key screws with T25 drive, grade 8 and proper heat treatment for durability and secure fastening