Faxon Firearms Bolt Carrier Group, 5.56NATO, Fits AR-15, Chameleon PVD Coated Bolt Carrier and Gas Key, Salt Bath Nitrided Bolt, Black FF556BCGCNITRIDE-NCR Seeing MIL-SPEC as just the starting point" they set out to ensure the best options are available for their demanding customers. Improvements include using 9310 tool steel for the bolt" nitriding the assembly to increase surface hardness" decrease resistance" and have superior corrosion resistance compared to typical chrome and phosphasted bolt carrier groups. All bolts are fully MPI tested to ensure the material is sound and without defects. Bolt lugs are chamfered 45 degrees to ensure reliable action for even the highest pressure hand loads and fast lightweight actions.