I guess my rifle ammo pick is for availability. You are far more likely to find a group with 5.56 and 7.62 if the boog really does light off over the other calibers. I'm probably in a bit of a pickle with the .40 but meh its a last ditch personal defense weapon so no real need for crates of it lying around. I prefer it for the capacity of a 9mm but the stopping power a .45 along with the better ballistics.