How did the Las Vegas shooter fire so many rounds of ammo?

HOUSTON (FOX 26) - Less like a concert, more like a gun battle. It seemed like the rapid fire shots would never end. Firearms expert Cris Parsons used to deal machine guns and doubts the Las Vegas shooter was using one.

"I hear a lot of inconsistencies in the cadence which is the rate of fire and that leads me to believe it could be one of those makeshift devices. Like a bumpfire stock or a hand crank you put on the trigger," Parsons says.

Both things are easy to buy and far cheaper than a machine gun, which can cost tens of thousands of dollars, and sources, according to the Associated Press, say that's exactly what he did have.

His trained ear can detect more than one type of gun being used. He thinks the shooter was constantly switching weapons.

"You can't take a rifle and shoot it rapidly, it will just overheat and it will overheat and get to the point where it will malfunction. That's probably the reason he had multiple weapons," Parsons says.

He says besides, getting a machine gun is tough even if you have the money. The Feds have to sign off on every sale.

"Six months. Two years wait time. I've seen it take three years waiting on approval before you can take possession of the gun," he says.

We won't know about the weapons until authorities release more information They are trying to trace the guns to find out where he got them. Typically they take the serial number, find out to whom the manufacturer sold it and find out to whom the store sold it. Parsons says that can be quick unless......

"Now if it's something I bought at a gun show they'd have to trace back and find a dozen people before they find out how it got into their hands."