Q Two-Piece Bolt Carrier Group Black. Most BCG's on the market today do not meet Mil-Spec standards one way or another; but ours not only exceeds the specifications but the design and size of the Front end makes it easier to control the manufacturing of critical features. Smart people stuff. The Two Piece BCG is designed to be manufactured on modern equipment using modern materials. Specifications for Q Two-Piece Bolt Carrier Group: Manufacturer: Q Color: Black Finish: Black Nitride Fabric/Material: Stainless Steel Bolt Material: Nitride Caliber: 5.56x45mm NATO Gun Make: AR Platform Package Contents: Q Honey Badger Two-Piece Complete Bolt Carrier Groups Q ACC-HB-BCG-2PC-MP: Two-Piece Bolt Carrier Group Black