Yes you can put a longer barrell on your gun, just make sure it's for the same model gun. I know they used to even make muzzle loader barrels for them. just remove the barrel and put the new one out. As far as the length I don't shoot buck shot so i'm not sure. Also keep in mind that your range is going to be limited with the buck shot, the couple guys I know that use it only shoot about fifty to sixty yards max with 3.5 inch shells, but in the areas they hunt they won't be able to get a shot that far anyways.