Self-defense expectations: "normal" vs. abnormal
If this reflection is merely a boring rehash, please forgive me and ignore the post: I've been thinking of late about the contrast between the "average" kind of self-defense incident (e.g. for example, those cited monthly in NRA publications) vs. the extrordinary kinds of events we've all witnessed in national news (e.g. the determined suicidal shooter who assulted the Denver area church). It strikes me that the self-defense needs between these two scenarios are very different.
I can't remember reading about an incident in which an "average" self-defense episode required a reload. Nor, for that matter, can I remember any of these "average" encounters that wouldn't have been suitably served by a good old "J" frame stuffed with appropriate ammunition. (I'm not trying to restart any arguments here, merely making a point. Stay with me.)
On the other hand, I suspect that many of us are beginning to think about the the "extrordinary" incident-like the suicidal maniac who attacks the mega church, or the deeply disturbed teen who decides to play "Terminator" at the mall. It strikes me that the expecations between "average" self-defense needs and "extrordinary" situations give very different answers to the kind of arm one may choose to carry, number of rounds carried, etc.
My personal expectation as a civilian, is that my primary responsibility is to protect myself and my loved ones while I seek to withdraw from trouble. Still, if a "terminator" began shooting at everybody in sight while I was at the mall, I'd personally feel more comforted by the precision, reach and capacity of my Sig P220 over my trusty 642. Thoughts?
Longer range, significant caliber
I think you have a point. While a small, short range gun with minimal sights might be adequate to handle the mugger armed with a knife, a suicidal person who wants to kill dozens before dying himself is a different situation. The latter person is more likely to be armed with a semiautomatic rifle or two pistols, have lots of ammo, and be wearing a bulletproof vest. Possibly the only way you can bring him down might be a head shot from 50 feet or more.
Your one advantage could be that the shooter is not specifically focused on you, but rather on many targets in a large arc around himself, so that you might be able to take a careful, aimed shot from his side or rear before he realizes you are there and are armed.
The other possibility is that he is coming right at you, and you might have to fire many shots at him from the front, while taking return fire from him, to bring him down. And again you could be engaging him at a distance of 50 feet or greater, so that accuracy is paramount.
In this situation I don't think I would want my S&W 642 snubby or my Kahr MK9, neither of which are long range guns with significant ammo capacity. I would rather have a .40 or .45 with 4 to 5 inch barrel and more rounds in the gun. And I'd want it to be a gun that I had practiced with extensively and was accurate in my hands. Of the carry guns I have used personally, I'd pick my Sig P229 in .40 or Kimber Pro in .45.