Bergara ST1 (self timing) muzzle brake - 6.5 caliber the ST1 employs an angled baffle design that applies downward pressure while not venting gas into the line of sight or increasing ground disturbance. This results in a drastic reduction of felt recoil as well as minimal muzzle rise. Features: Best in class recoil and muzzle rise mitigation Includes wrench and bubble level 1.1 inch locking nut diameter