well to reply to the head shoot thing...
A hard time of programing, but with great reallisme, there could be a thing like : 1 head shoot kill, (depending of weapon) body shoot kill, and so on.
So for exemple if I have 100 health, well 1 head shot and am dead. With the ruger (for exemple) 2 to 3 shoots to the body and I die.
So depending of the place we shoot , life will go out faster or slower.