If you are legally justified in using deadly force, you had better make sure that you use TRUE deadly force. Shooting someone in the arm or leg opens the door to a charge that you "really couldn't have been in fear for your life, or you would have killed him." So even if you hit the guy in the leg, you had better claim that you were aiming at his chest! On a more practical note, if someone is truly threatening your life and you shoot them in the leg, even if you sever their femoral artery, there is enough time for them to kill you. The best rule of thumb is to use the F.B.I. standard, also adopted by many departments across the nation: You do not draw your weapon unless you intend to use it, and you do not fire it unless you intend to kill someone.