NJ, the legal standard is normally just a bit tougher.
It's not what YOU believe, although that is part of the evidence taken into consideration.
The standard is what would a reasonable person have believed, if put into the same situation, and given your knowledge of the event.
So, you should be able to articulate why you believed what you did, and authenticate it with details. Documented training can help you, here. Otherwise, the rules of evidence may or may not allow your lawyer to draw out your specific knowledge. (For instance, you'd have to prove you knew about the Jared Reston incident prior to your SD event, if you wanted to tell the court about your knowledge of an instance where both the officer and the bad guy hit each other 7 times, with .45acp, before the gunfight ended.)
"But you shot him five times! Surely that shows intent to kill!"
"I was trained (in class X by instructor Y) to shoot until threatening behavior stopped. He had a weapon pointed at me, and did not drop the weapon or attempt to leave. I have read many cases where assailants continued their attack after having been hit multiple times, and believed he still posed a mortal threat to me and my family. When he fell, and ceased his attack, I stopped shooting."
That kind of thing.