Ballistics and such...

"Lethality comes in threes, you need to accurately hit your target. The "center of mass" hold for pistol shooters is fine for a high probability of lethal effects, but it is almost a guarantee that a center mass hit will not "stop" an attacker. To stop an attacker you have to get a central nervous system shot, brain or spinal column, to get a guaranteed stop."

AmMerc has a good piece on ballistics....HERE

I could not have said it any better...