Geissele Reliability Enhanced Gas Key and Bolt Carrier. 56mm full-mass full-auto rated M16/M4 bolt carrier group manufactured in Geissele s state-of-the-art manufacturing facility. The carrier features a properly torqued and staked Chrome Lined Nano coated gas key. 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. Specifications for Geissele Reliability Enhanced Bolt Carrier and Gas Key: Manufacturer: Geissele Color: Black Caliber: 5.56mm Package Contents: Geissele Reliability Enhanced Bolt Carrier and Gas Key Geissele 05-2992: Reliability Enhanced Gas Key and Bolt Carrier