“The critical element is penetration”
I’m guessing he carries a 9mm.
The critical element is hits.
Coming away from it, I pretty much determined he’d carry a Remington 870 shotgun, if he could, as pistols are pretty well useless for immediatley stopping a threat (which is the goal).
One fact that was interesting to me was “knock down” being a fallacy — the energy from a 9mm and .45 being effectively the same — about as hard as a lobbed baseball.
The key in stopping was permanent wounds, which favored the larger weapons -— but any of them with a heart shot -— the person had 15 seconds or so of life to ruin your day.
In short, unless you got a head or upper spinal cord shot, keep shooting.
This is an old study by Fackler. Worth reading for anyone who hasn’t read it yet?
9mm? No. If you read the last paragraph it concluded that penetration stops and the bigger the hole the better. Nothing wrong with 9mm but the bigger the hole the better.