https://www.yahoo.com/news/first-look-guns-used-las-vegas-shooters-hotel-room-163623120.html
No drums here. Large capacity magazines.
That first, continuous 10-second sting I analyzed consisted of far more rounds (120) than any linear magazine can hold and feed reliably.
FULL DISCLOSURE: I have not yet analyzed other audio. It could be that on that first string he used a weapon that was "not like the others"...
Forgot Magpul made the 100 rd mags.