Designed for the AR-15 platform. Stage 2 group is a significant improvement over conventional manganese phosphate and hard-chromed bolt carrier groups. Nickel Boron (NiB3) coating is more durable (resists abrasion and corrosion), more uniform (.0001-.0002 inches tolerance), reduces friction (.04 friction coefficient) and easier to clean than conventional manganese phosphate-coated and hard-chromed bolt carrier groups. Includes BHIâ€™s Lightning-Lok Titanium firing pin with Titanium Nitride coating. Due to the firing pinâ€™s inherent lubricity and lighter weight versus conventional firing pins, lock time is reduced thereby decreasing the opportunity for shot disturbance. Complete ready-to-go assembly designed to work in all AR-15 rifle platforms chambered for 5.56mm NATO. Includes the carrier, bolt assembly and extractor, staked bolt carrier gas key, Lightning-Lok firing pin, firing pin retaining pin and bolt cam pin.