as stated earlier,it all depends on the load you want to use.the tube you have is about what is recommended for the hevishot..660-670 is typically for #6,#5,#4 lead shot.hevishot normally likes .670-675.i shoot #4 hevishot and nitro 4x5x7 with a .670 and am very pleased at 50 yards.both my 870 rem and browning a500g shoot hevishot well with .670 tubes.don't pattern your gun at 30 yards except to make sure your sights match the barrel.always shoot 40-45 yards to find your maximum range.