Do look at your local laws, too, for instance, in AZ it is legal to carry concealed any lawfully owned firearms on the National Registry. We also have a very simple law stating NO civil liabilty for justified conduct. If I use a Serbu Shorty or AC556 in self defense, and it is ruled as such, the perpetrators family may not sue. Period. Would I use such? No, can't afford anything NFA, for one, and the fact that a full auto firearm is highly likely to sway the grand jury against the user.
It is legal, and you do have many legal protections in AZ, including Castle Doctrine, but I'd rather not do it, myself.