I also was just informed there is a way to make an AR-15 basically full auto legally. Was not aware of the new stuff they come up with.
Reddit commenter FWIW
“It definitely wasn't modified semi-automatic rifles.
Even with a trigger modification, the upper receiver isn't designed for that volume of rounds, and would have jammed. The barrels would have melted pretty quickly too with that rate of fire.
I've fired the M4 (AR military variant) on three round burst, and that thing jams all the time. And that's only three rounds. And it's designed for that!
Half an hour of sustained fire, mag after mag? Had to be fully automatic. Likely several fully automatics.
One other issue: how were the gunshots heard over the concert music from the Mandelay, 1500 feet away? I can't hear s** five feet from me at a concert.”
And another-
“From everything I've heard described (particularly the range, kill ratio, and volume of fire) this sounds like more than an ordinary military assault rifle firing full auto. Given the range and effective kill ratio, it sounds 30 caliber (e.g., .308) instead of merely .223, and given the hundreds of rounds fired by presumably one person in a relatively short period of time, that would seem to indicate a belt-fed instead of magazine fed. IOW, this all sounds like the kind of carnage of a belt fed, 30 caliber M60 machine gun.”