Question, how much influence on weapon choice do you attribute to the media/ politician focus on "semi-automatic assault weapons" in such circumstances?
In general, an AR15 (even a pistol) is much larger and harder to conceal. Parkland shooter for instance, couldn't fit the magazines in his bag and had to use 10 rounders because of size. Likewise, the Las Vegas shooter with the rifles with bump stocks had what, like 8 rifles? From what I recall, he had plenty of money and could probably have bought a real machinegun, or illegally converted his stuff. The bump stock is probably a detraction from what he was doing.
But, I mean, he also could have bought a belt-fed or one of the crank/ rotary guns, rather than using a finicky bump stock, so he obviously didn't do much research.