Sadly, in a lot of cases, perception trumps reality. And using a rifle, particularly a military look alike rifle, by choice, can give the otherside the opportunity to try and convince the jury of something that isn't really so.
They can try to make it look like you were eager and looking forward to shooting someone. They try to do this with handloads, or a gun that has been customised, or anything that they can use to imply that the shooting wasn't a last resort action.
Use of a military style rifle, particularly when it wasn't the only gun available will be pointed out as "proof" you were anticipating a confrontation (at best) or that you were actively looking for the chance of shooting someone (at worst).
Something like "a regular handgun wasn't deadly enough for you, you chose to use an assault weapon!" etc. Anything and everything is grist for their propaganda mill to paint you as irresponsible, and therefore, in the wrong.
Leaving aside the fact that for most home defense situations any rifle is overpowered, over ranged, too long for best use inside the house etc., etc., etc.....the fact that you chose to use an "assault weapon" (and they can get away with calling it that, because, under several laws, it is defined that way), iis going to be used to play on the emotions and sensibilities of the jury.
Even though I live in a rural location, where a rifle is actually somewhat useful for "home defense" (and that includes predator and varmint control), for self defense against human attackers its a very very unusual situation where you would be justified shooting them at rifle ranges.
At close ranges, particularly inside the home, the rifle (even a carbine) has distinct disadvantages over a handgun, or a shotgun.
But, if its the only gun you have, or its the only one you can get to in time, that's what you use. Just be prepared to have to counter the "evil" image the other side is going to make it out to be in court.
A tricked out AR, with a 30rnd stick in the well creates the image of "offense" more than "defense" in the minds of the non enthusiast, and tis quite likely there will be more of them on a jury than people who actually understand firearms and their use has nothing to do with appearance.