I've always thought that the .22 was underrated for self defense purposes.

I think I saw a study once that the vast majority of shooting encounter occur inside of 7 yards.

At that distance, I can reliably empty 10 rounds out of my .22 into a melon sized space in a couple of seconds. When I shoot a .40 or a .45 I am not nearly that accurate or fast.

My analogy is that I have a very nice 12 megapixel SLR with a 300MM telephoto lens that takes amazing pictures. But there is no way you can tote that all the time. So I have a little camera the size of deck of cards that I always have with me and it takes pretty good pics too.