Sorry. It wasn't my intention to start an argument over caliber and "knockdown power". The best gun to carry is the one you have with you, as they say.
Also, someone mentioned the .357 magnum caliber. That is certainly a notable exception to the "bigger than 4" rule.
As has been demonstrated in numerous wars and police shootings, however, I think it really comes down to three issues, especially with handguns:
- shot placement
- the type of round (i.e. ball or hollow-point of some kind)
I'm not sure who mentioned it earlier, but that stuff about all the rounds penetrating the same into ballistic gelatin doesn't really matter to me. Gelatin doesn't shoot back. I have taken the time to read up on police and combat shootings and how the various rounds perform in the real world.
The last time I checked, although it's been a while, the 125 grain .357 magnum JHP had the highest number of one-shot stops. I believe the 230 grain .45 caliber came in second.
Neither the 9mm or the .38 caliber has a good reputation as a man-stopper in the real world. Have people died from them? Certainly. Would I trust my life to one of those rounds? No.