Estimates for trained soldiers have indicated that it takes from 30 (In urban combat_ to
250,000+ for Viet Nam, where rotary-machine guns were commonly used to kill an enemy.
In the heat, fear, uncertainty of a home/business invasion I doubt that we can expect too much more of citizens, even at the point-blank ranges in such events, as: The usual such "invasion" is by three thugs; And, it generally takes three+ rounds (Dependent on placement) to immobilize (Or kill) an enemy soldier or a criminal For those who have forgotten their grade-school mathematics: Three-thugs X Three rounds each = Nine rounds which is more than in Mr. Joseph Biden's double-barreled shotgun or the seven-round limit imposed by New York's pro-death (For law abiding citizens) Legislature and Governor.
Of course, an evil-minded persons could easily obtain a WMD as could kill or maim hundreds/thousands of persons----Without the technical knowledge applied by Timothy McVeigh in Oklahoma City or twice by Mohammedan terrorists at the Twin Towers in New York. (I will not list or describe these weapons here lest someone use them.) Of course any such act-of-tyranny as taking modern weapons away from the People might result in patriots using such WMD!