One of the elements that mil-spec AR-15 bolts are known for is their tendency to need lots of lubricant in order to continue running properly. However, this added lube can also attract dirt and retain more fouling, which can be a vicious cycle for those looking to make their ARs run right. Enter the ODIN Works AR-15 Bolt Carrier Group. Each ODIN Works AR-15 Bolt Carrier Group is treated with a black-nitride finish across all metal surfaces, which provides a low-friction surface that doesn't require as much lube to run properly as phosphate-coated bolt-carrier groups. The bolt-carrier group is designed for use with traditional AR cartridges that share the 5.56 NATO case head. The ODIN Works AR-15 Bolt Carrier Group features a bolt machined from case-hardened 8620 steel, while the bolt itself is machined from case-hardened 9310 steel. The gas key is machined from 4130 steel and is attached using Grade 8 hardware and features proper staking to ensure position and reliability. Other features include a 4340-steel cam pin, a 8740-steel firing pin that's hard-chrome coated and a 4340-steel extractor