The fact is, a single bullet may not bring down its target. It might require several bullets given the need to quickly drain out as much blood needed for the brain to shut down. That means the ability to effectively hit the target, who may be moving around and may be causing you to duck behind a barrier to avoid being shot. Opportunity may be a brief window. It may require several shots to do the job and automatic fire and large magazines insures that you will be successful with the little time you have.
Well you’re right, BUT...
If in the most extreme emergency, NEVER tell someone you were trying to KILL a perp, or drain their brain of blood, but rather STOP them.
“Officer Friendly, I was in fear for my life! I told him to stop! I said it repeatedly! But he kept coming!!! I just wanted to stop him. I was sure he was going to kill me if he didn’t stop.”