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.