Geissele Reliability Enhanced Bolt Carrier Group 5.56mm. 56mm full-mass full-auto rated M16/M4 bolt carrier group manufactured in Geissele s state-of-the-art manufacturing facility in North Wales PA. The carrier features a properly torqued and staked Chrome Lined Nano coated gas key. The cam pin is machined from an advanced tool steel also used to produce medical instrumentation known as H13 it is then coated with Nanoweapon (Chrome-Nitride) for maximum corrosion and wear resistance. The extended upper rails on the carrier also provide much greater stability and dramatically increase feeding reliability. The Carrier is coated with Nanoweapon for maximum corrosion and wear resistance. The Geissele Reliability Enhanced Bolt Carrier Group comes with the Geissele Stressproof Bolt. Each Forged bolt is rigorously inspected high pressure tested mag particle inspected and Nanoweapon coated. Specifications for Geissele 5.56mm Reliability Enhanced Bolt Carrier Group: Manufacturer: Geissele Color: Black Caliber: 5.56mm Package Contents: Geissele 5.56mm Reliability Enhanced Bolt Carrier Group Geissele 05-2993: Reliability Enhanced Bolt Carrier Group 5.56mm