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. FeaturesMagnetic Particle Inspected (MPI)Carrier machined from 8620 alloy, full auto profile, heat treated and a black nitride coatingBolt precision machined from 9310 alloy; carburized/case hardened, shot peened and parkerizedProperly staked gas key