Features a shot-peened bolt for increased surface strength and durability, and an extractor booster to ensure reliable cycling during rapid semi-auto or full-auto fire. Includes Colt M16 firing pin upgrade. Each assembly is magnetic particle inspection tested to ensure its free from imperfections that can lead to premature failures. Properly staked gas key prevents gas leakage that can lead to short stroking. Available in .223/5.56mm, .300 Blackout ONLY... Staked screws, melonited exterior with hardened interior for bolt and cam pin.