Description: Ballistic Specialties Beretta 391 Gas Piston. This increased performance Gas Piston is CNC machined from hardened 174-PH stainless solid bar stock Piston is extremely strong and won't break under the rigors of a day of hard shooting. Designed to replace the factory gas piston in the Beretta 391 Shotguns in 12 and 20 Gauge. Includes Gas Piston Bushing and Gas Piston Bushing Snap Ring. Will not fit any of the 3 1/2" 391 Beretta Shotguns. Some gunsmithing may be required.