Contrary to popular belief, .223 ammo is less dangerous (retains less energy/velocity) after penetrating a standard interior wall (two layers of sheetrock seperated by 3.5" of air) than 9mm, .40S&W, .45ACP, or #00 Buck rounds. It is an excellent round in many respects for home defense.
Two significant problems from your AR:
- High-velocity rifle bullets are LOUD, especially indoors. I strongly recommend electronic earmuffs (Pro-Ears are the best) if you have time to grab them. Better to be deaf than dead, but better not to be deaf if you can prevent that too.
- No matter what weapon you use on the bad guy breaking into your house, it will be confiscated after the shooting. You may or may not ever get it back, even if cleared of the shooting. That to me is the best reason to suggest a (relatively) cheap shotgun (with #4 Buck) over any expensive semi-auto rifle. Of course, the above will not apply in any SHTF/TEOTWAWKI scenario.
In any event, keep all of your guns except your primary defense gun(s) locked away (in your safe, preferably) so that if you ever DO have to shoot someone, you won't have your entire gun collection taken from you (this happens routinely).
-Troy