Kaw Valley Precision Blow Back Bolt Carrier Group BCG .40S&W/10mm Caliber Black Medium. Our BCG is compatible with Glock style magazines. The carrier is constructed of 8620 steel with a Nitride QPQ finish. The QPQ finish offers excellent wear and weather resistant properties that are superior to lower grade phosphate finishing processes. We ve added a beefier firing pin retention spring to help lower the likely hood of firing pin breakage. Specifications for Kaw Valley Precision Blow Back Bolt Carrier Group (BCG): Manufacturer: Kaw Valley Precision Color: Black Finish: Nitride QPQ Fabric/Material: 8620 Steel Carrier Material: 8620 Steel Gun Make: Glock Condition: New Package Contents: Kaw Valley Precision Blow Back Bolt Carrier Group Kaw Valley Precision KVP-40-SW-BCG: Blow Back Bolt Carrier Group .40S&W/10mm Caliber Black Medium