The Beretta Auto model recoil reduction unit not only reduces recoil, but serves as a "swing thru", weight to smooth the swing and carry the gun thru the target with less recoil and muzzle bounce.  This unit replaces the forend cap on the end of the magazine tube. 

Model #390...........(adds 7 oz. to the gun)

The 390 KIT includes both the 390 Reducer and the 7 oz. 390 Stock Weight

(The 7 oz. stock weight will bring the factory center point of balance back when used with the 390 and 391 reducer.  Easy to install, just unscrew the stock nut and screw the stock weight on.  Polished and blued steel.)