50 shots and nobody dead tells me 2 things; Either this shooter had no idea how to shoot, or they didn't want to actually kill anyone.
An AR15 is an extremely accurate hunting rifle that fires a .233/5.56 bullet. 50 shots would be a mag dump + 20 shots (possibly a drum mag?).
Even an average shooter (like myself) with an ar15 can put one in the chest at 100-200 yards.
What I am saying is thankfully this person was inexperienced, or unwilling to kill, because 50 rounds could have lead to multiple fatalities. Hope those injured pull through ok.