The MUR is a rigid Mil-Spec flat-top upper made to fit all AR15/M16 M4 rifles and carbines. The MUR was developed to give the customer a Mil-Spec correct upper receiver with a thicker wall, making the MUR upper receiver a stronger platform. This more rigid upper receiver will increase accuracy and reliability, while extending the life of the interfacing components. The MUR-1A model comes equipped with a shell deflector and forward assist. FeaturesAircraft-grade aluminum construction 7075 Forging Stress relieved, heat treated, aged twice and cryogenic treated Hard coat anodized, black per MIL-A-8625 TYPE III Class 2 Precision machined and finished by hand Bore coated with dry film lube over the anodized surface Compatible with all Mil-Spec AR-15 parts and accessories