I dont own a Mossberg, but an awful lot of people do, so they must be doing something right. I personally would not advise shooting the 3.5 inch shells in a pump gun. I have tried it and it will really ring your bell. Unless you are truly impervious to recoil then I would say shoot the 3" or 2.75" shells. With the improvements in shotshell performance and better chokes they will kill just as effectively as the long shells. If you want to shoot the long ones then I would say save your dollars until you can get a gas operated semi-automatic. Good luck whichever way you decide.