I always thought the same thing. A sawn off, dbl barrel 10 or 12 gauge riot gun or street sweeper in a classroom would be a real slaughterhouse.
Add in the delay before leftist sheriffs actually enter the building, and anyone hit by a shotgun is sure to bleed out. You can survive an AR-15 hit to quite a few parts of the body. I wouldn't like it, but you can live through that. Shotgun blast with medical care delayed? That would do to a person what Barack Hussein did to our country.