SilencerCo Fits Harvester Big Bore, 5/8X24 Muzzle Brake, Black AC857 This 3-port muzzle brake is compatible with all SilencerCo ASR Mounts and with multiple thread and caliber options, you can shoot suppressed for any demand. It offers quick and easy one-hand-on, one-hand-off attachment and detachment. The 3-port design effectively reduces felt recoil and muzzle climb. Each ASR muzzle brake comes with a shim set and rocksett for easy application.