AIM H4 AR/M16 5.56/.223/.300 BLACKOUT complete Bolt Carrier Groups. Features UCT's exclusive Nickel Boron EXO Technology coating and H&M's BLACKNITRIDE finishes. 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. Features 9310 Bolt Material; 8620 carrier; Properly staked machined billet gas key hardened to USGI specifications fastened with Hardened Grade 8 Fasteners; Shot peened MPI (Magnetic Particle Inspected) Bolt. Extractor insert installed. Proudly made in the USA with a Lifetime Warranty.