The Griffin Armament Enhanced 5.56 Bolt Carrier Group is fully billet machined from premium materials and finished in a QPQ Melonite for improved lubricity and surface smoothness. The carrier is machined from 8620 steel and the bolt is machined from 9310 steel. The bolt is properly heat treated, shot peened, and ground after heat treat. The cam pin and extractor are machined from 4340 and features the latest 15,000 round extractor spring design with a Crane O-ring for long term reliability. The gas key is installed with Permatex and staked per military specifications. The Griffin Armament Enhanced Mil-Spec Bolt Carrier Group is built to last a lifetime.Features: 8620 carrier 9310 bolt Shot peened, MPI, and HPT 4340 cam pin and extractor 15,000 round count rated extractor spring Crane O-ring Fully billet machined Melonite QPQ finish Properly staked gas keyGriffin Armament produces serious use products with exceptional quality at a fantastic value. Designed with real world experience and built in the U.S.A., their product line has the parts you need. They're built to last a lifetime and backed by their perpetual lifetime warranty.