I think we are getting caught up in the details of the gun, when that seems a bit like a dead end. Whether it was illegal or not, modified, etc. is going to mean very little because you will have one side crying out for gun control and the other (NRA) side shutting down any notion of that sort. It will get us nowhere, and I see it as pointless. Besides, is it really any better if he has to fire slower? The guy was in an elevated position and there was no simple way to get to him.
I'm more interested in what hotels will be changing and how will large concert venues handle security differently. Bag checks? Cameras in the rooms? Metal detectors?