On the plus side, a .22 semiauto pistols have such light recoil you can rapid fire 10 shots into a tiny group in a very short time. You just need one with a decent trigger. Ruger 22/45, S&W 22A and the like.True. My dad helped feed his family of five siblings and four adults during the depression by harvesting deer by shooting them in the head with a .22 rifle. My mother helped feed the family by shooting giant snowshoe rabbits in the head in Alaska right after WWII. Many/most deer poachers even today probably often use .22s because the sound doesn't travel far compared with major calibers. I ran into one guy who was living almost totally on poached deer. He shot them in the head with a 22 rifle. Any other shot and the deer runs too far before dying to find in the dark.
SD with a .22 is different issue from effective hunting, as if you are under attack from a human mere feet away, for example, you need instant incapacitation. And a chest shot or several with a .22 won't usually incapacitate fast enough unless its a brain shot. Even .357s and 9mms frequently don't incapacitate fast enough for SD purposes with chest shots. For SD using a .22 I figure all brain shots. For SD with a .38sp or equivalent or better I practice first two shots to brain, the rest to the chest. This is also useful if bad guy is wearing a vest.