Las Vegas Shooter Possibly Modified Guns With 'Bump Stock' To Rapidly Fire Rounds

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LAS VEGAS (CBSMiami) – The ugly sound at the Las Vegas massacre – the sound of automatic weapons.

Or were they?

To Henry Andelo's trained ear "it still seemed a little off."

Clark County Sheriff Joe Lombardo confirmed Tuesday that a "bump stock" or "bump fire" was found in gunman Stephen Paddock's hotel room.

"They came out that it was a bump fire and it kind of made sense. It was a little irregular how he was shooting," said Andelo.

Lombardo did not specify whether one or more of the bump-stock devices were found, and wouldn't comment on how the weapons were modified, saying the Bureau of Alcohol, Tobacco, Firearms and Explosives is investigating.

Pictures from inside the shooter's suite at the Mandalay Bay Hotel appears to show one of the guns had a bump stock installed.

The ATF has said it is conducting an "urgent trace" on the firearms.

Authorities said Paddock opened fire from the windows of his 32nd floor hotel room late Sunday, killing 58 people and wounding hundreds more at a country music festival. Police stormed his room and found he had killed himself after committing the deadliest mass shooting in modern U.S. history.

Witnesses and law enforcement official said the quick, 50-round bursts of gunfire raised the possibility that Paddock had used a fully automatic weapon or modified his semi-automatic rifles to function like one.

The device basically replaces the gun's shoulder rest, with a "support step" that covers the trigger opening. By holding the pistol grip with one hand and pushing forward on the barrel with the other, the shooter's finger comes in contact with the trigger. The recoil causes the gun to buck back and forth, "bumping" the trigger.

Technically, that means the finger is pulling the trigger for each round fired, keeping the weapon a legal semi-automatic.

"What happens is the guns move back and forth in the stock. Every time the gun fires it recoils back a little but into the stock itself and because you have your finger in the key position it fire like that," explained gun range owner Frankie McRae.

The bump fire or bump stock has little practical purpose. Shooters call them "range candy" – something to show off with.

But a weapon modified with the device, which can cost just over $100, can cause catastrophic damage.

"The military almost never uses full automatic. They only use it in the most extreme circumstances," said Ed Davis. "So the difference between flicking the lever up or modifying the weapon is the difference between killing four people or 40 people. That is really the difference."

Though legally and widely available, the so-called "bump stocks" have attracted scrutiny from authorities and lawmakers in recent years.