AIM AR/M16 5.56/.223/.300 BLACKOUT caliber complete Titanium Nitride and Nitride Bolt Carrier Groups. The Bolt Assembly and Gas Key are Black Nitrided to keep the cost down. Titanium Nitride is an extremely hard ceramic coating used in aerospace and military applications that improves the maintenance, cleaning, edge retention and corrosion resistance of the bcg. Features; Shot peened, MPI (Magnetic Particle Inspected), 9310 Tool Steel Bolt; 8620 M16 carrier, Properly staked 4140 Machined Gas Key fastened with Hardened Grade 8 Fasteners. Extractor includes crane o-ring. This is an Excellent Bolt and an Excellent Price! More details below.