Senate Democrats Wednesday introduced legislation to ban "bump stock" devices, which were used by the Las Vegas shooter to increase the rate of bullets fired on a crowd attending a country music concert.

Sen. Dianne Feinstein, D-Calif., a staunch gun control proponent, is the sponsor of the measure. It would "ban the sale, transfer, importation, manufacture or possession of bump stocks, trigger cranks and similar accessories that accelerate a semi-automatic rifle's rate of fire."

Bump stocks, according to gun experts, can be used to modify legal semi-automatic weapons in a manner that increases the firepower to that of automatic weapons, which are illegal.

"Automatic weapons have been illegal for more than 30 years, but there's a loophole in the law that can be exploited to allow killers to fire at rates of between 400 and 800 rounds-per-minute," Feinstein said.

"The only reason to fire so many rounds so fast is to kill large numbers of people. No one should be able to easily and cheaply modify legal weapons into what are essentially machine guns."

Feinstein introduced the bill with more than twenty Democrats, mostly from blue states.

The bill is the opening salvo from Democrats in their latest push for gun control legislation following the Las Vegas shooting.

If passed, it would be the most significant gun control bill to win approval since the 1994 ban on some military-style guns.

Republicans are mostly opposed to new gun control bills but Democrats are also divided. A bill to ban many types of military-style guns and high capacity ammunition clips, proposed by Feinstein in 2013, drew opposition from at least 15 Democrats at the time.

Republican leaders this week brushed aside calls for quick action on gun legislation because, they said, it is too soon after the shooting to consider whether they should do anything.