The shorter ammunition will work perfectly. The three inch 20 Ga. Chambering is the standard here in the US,for modern guns . We commonly shoot 7/8 ounce #8 in 2 inch(70mm) @1210 fps shellcases for clays and small birds like Quail. For Wild Turkey and Waterfowl I would use up to 1 ounce and larger shot in a 3 inch (76mm) case @1185fps.