Shotguns shoot their loads at a virtually uniform 1100 fps. British double rifles of the .450 NE, .470 NE, .450 #2NE, .475 NE class at the turn of the XX Century featured 500 grain bulletw at velocities of around 2150 fps. One and an eighth ounces of shot weighs almost exactly 500 grains. Doubling the velocity, while leaving the other variables the same results in four times the recoil, since recoil varies with the square of the recoil velocity.