Looking at the OF Mossberg WS, it is a new style lifter, bolt carrier and an "energy absorbing bumper". A $17 OPSol Mini-Clip allows you to shoot the Mini shells, but you cannot alternate loads in the same tube. If the the Mini-Clip is in, it is a 1 3/4" gun only. Pop out the Mini-Clip, and you can shoot the 2 3/4" & 3" loads.