American Built Arms A*B Pro 5.56 Bolt Carrier Group is built to Mil-Spec dimensions. The Nickel Boron coated Bolt and Cam Pin needs virtually no lube during use. The Nickel Boron coated Carrier is coated for extra lubricity and the phosphate coated extractor has a surface finish that provides superior extraction during firing. These Bolt Carrier Groups are ready to drop into your rifle. American Built Arms' Bolt Carrier Groups are specially made on high end Swiss machinery to have exacting tolerances and surface finish. FeaturesHeat treated, shot peened, nickel boron BoltM-16 style, nickel boron, 8620 steel Bolt CarrierMil-Spec, nickel boron coated, 4130 steel Gas KeyHeat treated, nickel boron coated, 4340 steel Cam PinHeat treated, shot peened, E4140 steel with manganese phosphate coated ExtractorChrome lined, AISI 8740 steel Firing Pin