A .22 isn't a self defense weapon because it has no real stopping power (the bullet weighs only 39 grains, vs. 230 grains for a .45ACP). But, it's a good assassination weapon provided the killer can put it right on the victim's head. It's small and concealable, has practically no recoil, and makes little noise. You saw a perfect example in "Casino," when Nicky (Joe Pesci) uses a .22 to kill a woman who was making trouble for the Mob-run hotel.