I find it interesting that just about everyone now considers a high-capacity autoloader to be, if not an absolute requirement for personal defense, at least the ideal to strive for. You hear it from the police brass too, when they whine about how they "need" MP5s or full-auto M4s in every patrol car because they are "outgunned" by AK-wielding gangsters.
In my opinion, a hi-cap pistol has one purpose: car defense. If I am practicing evasive driving while shooting to disable the car of an attacker bent on stopping me, I want lots of rounds in a gun I can handle and maneuver with one hand. Barring that unlikely scenario, I want an utterly reliable sidearm with substantial (for a defensive handgun) stopping power. To me that means a full- or midsized (L or N frame size) double action revolver in .357, .41 or .44 Magnum, .45 Colt, or .44 Special+P. .45 Auto or 10mm in full moon clips works, too. And if possible, I don't like to be too many steps away from some kind of longarm.
Here's my thinking: assuming you can shoot, if you get in a defensive situation where 5 or 6 rounds doesn't resolve the problem, you are not going to live though the encounter. Of course, if you can't shoot and neither can your adversary, you may indeed fire 17 or more rounds and live to tell about it, but then you will probably be "telling about it" in both criminal and civil court, because those bullets don't just vaporize when they don't hit your intended target.
Allow me to explain that in more detail. If a guy attacks me with a 17-shot 9mm and he gets one into my center of mass, I probably will not be able to fire very many rounds of my own in response, at least not effectively. And my lack of effectiveness would probably give him a perfect opportunity to put a few more into me, no matter how many rounds I have at my disposal. On the other hand, if I get one round of .357 Magnum into his center of mass, he likewise won't be able to utilize the 17 rounds he has available. So with one assailant, the situation should be resolved one way or the other in less than 5 rounds if one or both combatants can shoot and uses an effective round.
If there are two assailants, the same situation applies except that one of them will probably run away when he sees his buddy go down, anyway. If not, with a 5 or 6 shot revolver you still have a couple rounds to serve the second assailant, too.
Now, as you envision multiple assailants attacking you so that you really need 12 or more rounds, keep in mind that they will all be attacking you at once, almost certainly from a distance of less than 10 yards. Can you get 12 or more rounds on target before any of them can shoot, stab, slash or hit you in the head with a baseball bat? Who are you; Superman?
By the same token, consider a cop armed with a Winchester .30/30 lever action, facing a thug with an AK. If he fires one round and hits center mass, will it matter to that cop that he has 29 more rounds? If the cop gets a round of .30/30 into the thug's center mass, will the thug be able to use his remaining 29 rounds?
Of course, if I ever get in a situation where I am barricaded against multiple armed adversaries, I want my AR-15. A high capacity pistol is not a suitable replacement.
