If we're going to worry about the "what if's" during a defense trial, a lot is going to have to do with what state and city you're located, and ESPECIALLY what kind of guy you are, and have been in the past, and why it was necessary to use deadly force. I personally can't imagine ever pulling a gun on somebody during a fistfight, or shooting somebody who was running off with my property.....even if the POS of a human WAS on my property! You know, people kill other people all the time over stupid crap like that, and we wonder why they have to do the acadamy award performance of a lifetime in court?
And in the event anybody DOES rightfully have to use deadly force.....never mind the fine print that the prosecutor is reading off of the LEO magazine......I'd be more concerned with winning sympathy from the jury as to why I was using an AR15!
Frankly, I can't imagine ever having to reach for an AR15 in self defense, unless we have some really serious civil disorder. (katrina style flooding, nuclear attack, etc) My licensed handgun being called into action to thwart off a knife or gun threat by some slime ball is a much more likely scenario. Then it would be a case of my spotless record and Hollow points VS the druggie with the $19 gravity knife and a rap sheet as long as a roll of toilet paper.