A very important note to add with ballistics is actual ft/lb (Newton/Meter or whatever for the metric crowd) of energy delivered with the package. Comparatively a 9mm to a .45 is the greater muzzle velocity (not always, as this depends on the specific load). I would much more prefer to hit the numbers on impact than speed from the muzzle. Granted 9mm is the cheapest and most universal cartridge, and when it goes down to the actual trigger time e=mc2 and the human body is rather frail in defense to such a law.
I know, I have looked at quite a few charts on blastic data, some when I took my CCDw class. Depending on what chart you look at even a .38 can meet the minimum for a one shot stop.
For me 9mm is my choice over a .45. Due to cost and magazine capacity.
Now what happens when impact is made? Ball (FMJ), half-wad, or HP? Personally I stick to half-wad and HP for lower penetration and increased spall. I want one shot at center mass to end all questions as to who is in charge.
Thats expansion VS penetration. I have seen quite a few reports where .45 FMJ and 9mm FMJ never left a exit wound on a target.
Most people say 12-14 inches of penetration is optimal, that's when you get deep enough to hit a organ.
I am fairly sure a 9mm Hp will hit 12 inches easily and it will make a nice wound cavity.
Everything I have seen or been thought is always "shoot until the target goes down" you don't always get a one shot stop.
If I had to compromise I would settle for a .40 or 10mm HP in the pistol category. For a revolver definitely choose a magnum load; 125gr max HP or half-wad to eliminate over penetration and possible peripheral damage to property or innocent bystanders.
I dislike the .40SW (or short and week some call it) after shooting a few 100 rounds.
With the rate of misses to hit in most encounters over penetration and bystander/property damage is not really a major factor IMO.
Look at how many times cops miss in a shoot out when they happen.
And as far as shot placement, let this stand; Your objective is one round on target, or at most a double-tap. Accuracy is moot as most encounters in self defense are within 10-20 ft. A ten inch shot group center mass for a revolver vs 5 inch for a pistol becomes insignificant with the proper load.
I agree, you always hope for a one shot stop, and yes most encounters are very close. You would be surprised how much things change when you are moving and the target is moving, the hit % drops drastically.
I know I won't be standing still and the other guy won't either.
Very true. Revolvers are your best bet in a tight spot as they fail less often (and are much easier to maintain) and in general can deliver a much more powerful load. Always go with this option for personal defense. And train, and train, and train.
We agree, revolvers are easier to deal with if you have a FT fire, but my semi-has never had a issue either.
But I would love to get a .38 or pocket .357 as a back up gun (BUG) just in case.
Pistols (semi-autos) are better for the uninitiated as they have recoil buffer, faster recover to target time, and can be loaded much faster (an importance based upon some laws).
If you get good with a speed loader you can load just as fast, but yes you are correct. its easier to have a preloaded mag and just swap than practice with a half-moon.
And beginners should stay away from rifles and shotguns for self-defense. Unless you're a fringe element that cares little for their interior decor.

The boom stick is the king for HD and pretty much every other situation for a reason.
With a good 870 you have a ton of options for SD.