Wilson Combat Bolt Carrier Assembly 5.56 NATO Low Mass Nickel Boron Polished NIB Stainless. The Wilson Combat Bolt Carrier Assembly comes in several different finishes depending on your shooting needs: nickel boron black nitride and parkerized. Nickel boron offers resistance against corrosion and increases lubricity which makes the bolt carrier easier to clean. Parkerized Bolt Carrier Groups have a manganese phosphate coating that increases the thickness of the bolt carrier. The black nitride coating is very durable and resistant to corrosion while having a smooth finish for easier operation. No matter what finish works for your needs these bolt carrier assemblies are drop-in-ready and feature a staked gas key. You are ready to go with just a few clicks. Improve your AR-15's action and recoil from the moment you pull the trigger. Specifications for Wilson Combat Bolt Carrier Assembly: Manufacturer: Wilson Combat Carrier Material: 8620 Steel Bolt Material: 9310 Steel Caliber: 5.56x45mm NATO 300 HAM'R 7.62x40mm Wilson Tactical .300 AAC Blackout .223 Remington .204 Ruger Gun Make: AR Platform Hand: Ambidextrous Condition: New Features of Wilson Combat Bolt Carrier Assembly: Bolt material is aerospace grade 9310 MPI inspected; Mil-Spec parts ensure a long service life; Machined ejector and extractor per mil specs; Full Auto carrier (see note); Drop in fit for any quality 5.56 case head based AR rifle (.223/5.56 NATO .300 Blackout .204 Ruger300 HAM'R or 7.62X40 WT) Package Contents: Wilson Combat Bolt Carrier Assembly C0-BCG-WCBCASM Wilson Combat TR-BCA-LM-PNIB: Bolt Carrier Assembly 5.56 NATO Low Mass Nickel Boron Polished NIB Stainless