+111

I suspect that the smallest adequate calibre depends in part on your mindset and training.

The very first gun-fight rule I was taught as a LEO was that if I was going to have to shoot someone, DO IT FIRST. That is, don't wait until you are already receiving fire yourself and the perp has his adrenalin level at least as high as yours.

If you shoot first and put the bullet in an effective place, you can get by with a smaller piece of ordinance.

I think the smallest thing I would want to use would likely by my "hideout", my Walther PP in .32 ACP. I can pretty effectively hide it in my large hand until I decide its time for the curtain to go up. Of course, I'd prefer my Glock 10 m/m with 16 Black Talons, but there are times and places it doesn't go with me.

And, I keep remembering two officers on the Phoenix, AZ P.D. They walked into a bar together looking for a known-to-be-armed 211 suspect. He was in there all right.

They both died there. He was armed with a .32 ACP just like mine. They both had larger bore, higher-capacity, semi-autos.

He shot them both first, before they even knew he was there.