This Bolt Carrier Group (BCG) comes fully assembled and ready to drop into most mil spec .450 Bushmaster Upper Receivers. All critical parts are coated with EXO Nickel Boron technology that provides permanents dry lubricity extreme durability increase wear and corrosion resistance. Our patented Nickel Boron coating will reduce friction and improve the overall performance of your rifle.Nickel Boron treated parts include: Bolt & Extractor (.458 SOCOM and .450 Bushmaster compatible) Bolt Carrier Extractor Cam Pin Carrier Key Firing Pin