The first homicide I worked was a 22 shot to the head, one shot stop. I seen a lot of head wounds over the years and never saw anyone survive a 22 to the head. Most people assume you get shot in the head you die immediately not so. Unless you hit the base of the brain what kills you is pressure. A hole in your head helps keep the pressure in the brain down as it swells. The bigger the whole the longer it takes to clog. One case that surprised me was a guy who got shot in the brain with a 357. He had a 38 cal hole on one side of his head and a much bigger whole going out. No way did I think he would survive but several months latter he walked out of the hospital. He didn't walk well but he walked, haven't seen any 22 head shot wounds do that. This is likely for two reasons first a small entry wound which quickly gets plugged with brains and blood clots. Second is the round doesn't tend to exit and will zip around inside the skull till it runs out of energy. Back in the day I carried a little Beretta 22 short for a back-up. Before I carried it I wanted to test it's penetrations power on some 2x4's. It went through three and lodged in the forth. I figured it would penetrate any skull I aimed it at. I think people get to hung-up on pistol calibers, if you want a real man stopper your talking a rifle cartridge starting about 308. When you get down to it none of the calibers that are practical to carry even the mighty 45 are truly man stoppers. Frankly what stops most gun fights is simply someone shooting back.