How the hell did one guy keep shooting continuously for 20 minutes?

[csziggy]

19. A video has to sound of regular shots, in a rhythym

Video at link: http://www.msnbc.com/msnbc-quick-cuts/watch/witness-records-gunfire-at-scene-of-orlando-nightclub-shooting-704045123938

Many of the witnesses said that at first they thought the gunfire was part of the music, it was so regular.

MSNBC also has this about the weapons:

What Weapons Were Used?

Mateen, who had security and firearm licenses, used an AR-15-type rifle and a handgun, both of them purchased legally, authorities said.

The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives said the weapons were bought in the last few days.

The AR-15, a semi-automatic rifle, has been used in many mass shootings in U.S. history — at Aurora, Colorado, at Sandy Hook Elementary School in Newtown, Connecticut, and just last year at San Bernardino, California.

Bomb-sniffing dogs alerted on possible explosives, but authorities said none were found.
http://www.nbcnews.com/storyline/orlando-nightclub-massacre/orlando-nightclub-massacre-what-we-know-about-attack-n590666

Maybe a DUer with expertise in weapons can tell us if the audio on the clip from MSNBC sounds like an AR-15 and give us an estimate of how many shots were fired during that segment?

Edited to add: There are already conspiracy theories about this being a false flag operation. I saw a number of them while looking for the video above on YouTube. One claims he's identified actors - but I didn't watch any of them so I don't know what whacko ideas they are coming up with for this tragedy.