What if the Las Vegas shooter's weapon was perfectly legal?

OK, I'm not talking NFA firearm or illegally converted semi-auto, but a gizmo called "bump-fire".

This ties into my previous post about banning semi-auto.  Gunloons want to talk about "cosmetic" bullshit: we can get to functional.  These arms can be made to fire incredibly rapidly in a few ways

The rapid pace of the gunfire suggested that the shooter was using either a fully automatic weapon, tightly restricted under US law, or that he had attached a device to a semi-automatic gun to make it fire more continuously, said Massad Ayoob, a firearms expert, instructor and author. “It’s faster than almost any human being is going to be able to pull a trigger on a semi-automatic,” Ayoob said.
Fully automatic weapons, which fire multiple rounds of ammunition from a single pull of the trigger, are strictly regulated, taxed and tracked under US law. This makes them expensive collectors’ items, and comparatively rarely used in crimes. Semi-automatic rifles, in contrast, which fire only one round of ammunition with each pull of the trigger, are widely available.
Unlike some states, Nevada, which has laws generally friendly to gun owners, does not ban the sale of “assault weapons” – semi-automatic civilian guns built to resemble military weapons.
From listening to the footage of the attack, Ayoob said that the gunshots “did not sound as consistent” as he would typically expect from a fully automatic M-16 or AK-47. “The pace of fire is a little bit erratic. At one point it’s slower than it is at another point.”
Paddock could have used a Hellfire or a bump-fire device, which attach to normal semi-automatic rifles and allow them to fire more rapidly, Ayoob said. These devices are legal, but rarely used by serious shooters, he said.

As I said, these weapons are easily made to fire in a fully automatic mode and should be regulated accordingly.

See also:

•  Vegas gunman had device turning weapon into automatic - The Washington Post