AIM AR/M16 5.56/.223/.300 BLACKOUT caliber complete Nickel Boron coated Bolt Carrier Groups. A newly designed carrier reduces the surface area contact between the carrier and receiver walls. This improves performance and reliability as it reduces drag and creates 'debris' channels to reduce malfunctions. These bolts are manufactured to our exacting standards with no Frills added to be able to offer the best BCG at the Best Price! 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!