The Hollywood Mystique of a one shot stop with the bad guy flying backwards is hardly the reality. The tunnel vision, the adrenaline, the reactive actions the body goes through, especially those with minimal training, makes head shots improbable.
Law enforcement is trained to continue shooting until the threat is absolutely neutralized. Keyword is threat. My leetle .380 Kel-Tec, is not considered a whopping man-stopper by any means, but that is not the point, nor why I carry it.
The point is to end the threat. If it takes 3,4,5,6 a reload, and 2 more so be it. The end game is I'm alive, and the BG is not trying to end my life. If the BG expires,....so be it.
Notes from Col. Jeff Cooper come to mind.
"One bleeding-heart type asked me in a recent interview if I did not agree that 'violence begets violence.' I told him that it is my earnest endeavor to see that it does. I would like very much to ensure (and in some cases I have) that any man who offers violence to his fellow citizen begets a whole lot more in return than he can enjoy."
Jeff Cooper, "Cooper vs. Terrorism", Guns & Ammo Annual, 1975
"It’s our experience that in a fight you will continue to shoot the gun until the threat goes away or until the gun is empty."
"If you're not shootin', you should be loadin'. If you're not loadin', you should be movin', if you're not movin', someone's gonna cut your head off and put it on a stick."
From The Clint Smith, Jeff Cooper Memoirs.
Highly recommend finding them online and reading them...
http://myweb.cebridge.net/mkeithr/Jeff/