I like what Mr. Bluster said about the .22, but my understanding is that unless you make a headshot or sever the upper spine, your only hope of survival is to make the bad guy bleed out enough so he loses consciousness. The FBI paper on handgun effectiveness says a determined aggressor can continue his attack for 10-15 seconds after having received a mortal wound to the heart (http://www.firearmstactical.com/pdf/fbi-hwfe.pdf
). I would not expect most people to have the ability, in the heat of battle, to shoot the guy's head or sever his upper spinal cord. Without regular threat training in which the adrenaline is elevated and the vision's focus is narrowed, I don't think a person can count on their range training experiences alone. I believe I need to make the biggest wound possible to ensure rapid blood loss. That means multiple big caliber holes.