The Pistol-MUR is a rigid Mil-Spec flat-top upper custom made to fit Quarter Circle 10 carbines. The Pistol-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. Designed specifically for pistol-caliber AR builds in conjunction with VLTOR Mil-Spec construction Thicker receiver wall for increased rigidity and strength in blow back operation Widened ejection port for large pistol caliber pistol cases Made For the AR Platform- Not Modified 11.5 oz stripped weight *This product is not compatible with DI gas systems or rifle-caliber bolts