I haven’t read the number of rounds fired either, that info may not have been released. The rifle jammed and there were rounds left in the 100 round drum mag, he then fired pistol rounds. It’s probably safe to say he didn’t shoot too many more rounds than a hundred, if that.
The hype about him buying 6000 rounds is just that, hype, plus it was legal and those rounds could have been bought at a retail outlet or at a gun show.
Duh, that's why we need to limit sales of ammo *everywhere* (step 2 of the game plan)