The AR-STONER Bolt Carrier Assembly is the perfect choice for your next AR build! This AR-STONER Bolt Carrier Group has been machined to Mil-Spec standards and magnetic particle tested to ensure the assembly is free of any imperfections. This drop-in ready BCG features a properly staked gas key and is an affordable way to instantly increase the performance of your AR-15.Precision machined 9310 heat treated steel with a corrosion resistant black nitride finish. Full-auto capacity, shot peened MPI Bolt, 8620 gas carrier & gas key fastened with hardened Grade 8 fastners. Features:Machined to Mil-Spec StandardsProperly Staked Gas KeyComplete Bolt Carrier Assembly, Drop-In ReadyBlack Nitride Finish