What about 10mm?
Knock Down Power, remember Newton's 3rd Law of Motion, for every action there is an equal and opposite reaction. If a round could actually knock someone down, it would knock down the shooter pulling the trigger as well. Yes, what they really mean is probability the round would drop someone in his tracks from the trauma suffered by the round, which I agree with and use the term, just sayin, you're not actually knocking people down, you're dropping them in their in their tracks from the trauma.
Another way to look at it, which they seem to touch on in the article, a determined attacker will continue to try to attack you while they are dying. And even it it only takes a minute for them to die from their injuries, that could mean they may still have another 30 seconds to continue to attack you before they are incapacitated.... ....you want to cause an attacker enough trauma they are incapacitated as fast as possible...
And not to say bigger is always better, very true shot placement will have the biggest effect, I like the idea that if I'm off 9" in my shot, the damage will have enough effect to get close to the desired effect. i.e. I look at as there has to be a balance, not only shot placement, but amount of trauma caused for when you're off a little....
Muzzle Energy, i.e. Kinetic Energy, the formula is 1/2 the mass times the velocity squared.... ....I don't think the deadliness of the round comes down to simply how much kinetic energy the round has, there are all sorts of factors, but all other things being equal, more kinetic energy means more damage.... ....and kinetic energy halves the mass of the bullet and squares the velocity.... ...so muzzle velocity is the name of the game but mass is not to be ignored completely...
BTW, NATO 9mm is 124grns and MV of 1200 fps. It has a Kinetic Energy of 397 ft-lbs,
That is less than +P 9mm, but NATO 9mm is a little hotter than commercial 9mm.
So most retail 9mm have less K.E. than NATO and they vary.
Military .45ACP has less K.E. than NATO 9mm, but a lot of retail .45ACP has more MV than Military .45ACP.
Federal American Eagle .45 ACP has 404 ft-lbs of K.E.
