What they always fail to do is test the amount of deviation for each specific round. Sure, the 9mms performed close to the .40s, expanding an average of .1" less, penetrating a few inches more (a good thing, in my opinion), but upon hitting a rib, how straight did the wound path remain? A bullet will often hit a bone or something and may well deviate off course, going from a well-placed vital shot to a flesh wound, especially if that object is at an angle, as the bullet will encounter much more matter than if it was going straight at the matter.
What I'm getting at is, there are three reliable wounding factors.
First is penetration. You need to be able to reliably get deep enough. I think the more, the better. I would be more confident with an over-penetrating round, as if anything gets in the way, like an arm or something, I can be more sure that my bullet will still be able to reach a vital organ. In handgun rounds, velocity will usually lead to more penetration, all other factors being equal.
Second is resistance to deviation. If the bullet can go deep enough, can it go deep enough while going where I pointed it to? If it hits that hypothetical arm, encountering most of the forearm muscle, as well as a bone, will it remain on it's path towards the intended spot it was first sent to? Bullet weight is usually the deciding factor in the resistance to deviation.
Third is size of wound channel. Let's say you have the first two factors down, but the wound channel is small, there is a higher chance the bullet might squeeze it's way between vitals. Organs, nerves, blood vessels and arteries are close together, but even a shot to a vital organ can end up just skinning it. Even then, there is likelihood of the damage to the organ being insufficient, and not ending up with incapacitation. The main factors for a large wound channel is the proper bullet construction and it's diameter.
Now those are the terminal effects I look for. Things like "stopping power" (a term I HATE with all my might) and "energy" have an effect, but it's subjective to the target's state. Even the most powerful caliber with the most energy and the most insane punch and "stopping power" and "hydrostatic shock" (insert more buzzwords here) WILL NOT BE WORTH A SINGLE S****T IF THE VITALS ARE NOT REACHED AND SUFFICIENTLY DAMAGED. Only, I repeat, only the sufficient damage to vitals will lead to a sure and quick incapacitation.
Sadly, they conflict with the human factor of shooting successfully and accurately. Factors like recovery of sight picture from recoil, ergonomics of grip, price of practice ammunition, of firearm, and many many more come into play when choosing a caliber. But that's not what this is about! That said, I think a heavier bullet at high velocities with a reliable expansion and sufficient diameter is putting odds in favor.
CCI GD 9mm 147grs and CCI GD .40S&W 180grs would be my pick. Only a very hot loaded .45ACP of the right weight and type would float my boat and would fill my three terminal effect checklist. Still then, the .45's diameter makes it eat up magazine capacity, and makes double stack mags quite large, and it isn't so for .40s and 9s.
/ballistics rant.
Oh if I'm mistaken somewhere, I'll review my words if there's enough proof/justification.
