The groundbreaking MCR (Mission Configurable Rifle) belt-fed upper receiver assembly is designed to interchange with standard AR/M4 type uppers and readily fits any MIL-Spec lower receiver without permanent modification to the host lower, and is rearward compatible to AR15/M16 models produced as early as 1963. The MIL-Spec MCR 5.56 DFR takes their standard MCR technology to a whole new level and includes all of the accessory items that are included in their standard MCR government product along with Dry Film Lubrication on critical high-friction surfaces for extra performance in extreme conditions.