The WMD Bolt Assembly for 450 Bushmaster is engineered for optimal performance with NiB-X nickel boron coating that provides long life ease of cleaning and superior locking and unlocking action with barrel extensions.WMD Bolt Assembly - 450 Bushmaster CaliberCase Hardened 9310 Steel - Shot peened and magnetic particle inspectedNiB-X Nickel Boron Coating on bolt and extractor for durabilityHigh performance extractor ejector springs and gas ringsSpecial O-ring buffer for enhanced reliabilityDesigned for serious shooters who demand reliability and easy maintenance in their 450 Bushmaster platform rifles.