CMMG 94AC80FAB: Forget what you thought you knew about Pistol Caliber Carbines, the Dissent Br4 brings classic rifle ergonomics together with the fixed ejector Radial Delayed Blowback technology of our 9mm Dissent lineup. The 9mm Br4 uses our 9mm conversion magazines, which also means that the Br4 lower will accept other Stanag pattern magazines if you decide to swap to another Mk4 Dissent upper group.