An AR-15 rifle with a bump stock is shown on sale at Blue Ridge Arsenal in Chantilly, Va., on Friday. (Jim Watson/AFP/Getty Images)

A prominent gun-control group filed a lawsuit Tuesday against the maker of “bump stocks,” the devices believed to have been used by a mass shooter in Las Vegas to inflict maximum carnage when he opened fire on a country music festival last week.

The devices, which are legal, essentially allow semiautomatic weapons to rapid-fire bullets, much like an automatic rifle or machine gun would. A dozen rifles fitted with bump stocks were found in the hotel suite of Stephen Paddock, who killed 58 people in 11 minutes from his perch on the 32nd floor of the Mandalay Bay hotel on Oct. 1.

The Brady Center to Prevent Gun Violence and a private law firm filed the lawsuit in Clark County District Court on behalf of the 22,000 attendees of the Route 91 Harvest music festival, the event that Paddock targeted at the end of its final night on the Las Vegas Strip. The lawsuit alleges that Slide Fire Solutions — the best-known manufacturer of bump stocks — and others who manufacture, market and sell such devices were negligent in making them widely available. It seeks punitive damages for emotional distress inflicted on the concertgoers.

The assault “would not have occurred with a conventional handgun, rifle or shotgun, of the sort used by law-abiding responsible gun owners for hunting or self-defense,” the lawsuit alleges. “The damage caused to Plaintiffs resulted from the military-style arsenal that Defendants manufactured, marketed and sold to the general public, without any responsible measures or safeguards, and which the killer foreseeably used to such horrific results.”

The lawsuit heightens scrutiny of bump stocks since the Oct. 1 incident, now considered the most deadly mass shooting in modern U.S. history. The metal or plastic attachments harness a gun’s natural recoil, allowing it to bounce back and forth off a shooter’s trigger finger and unleash up to 100 rounds in seven seconds, according to an ad for one of the devices.

Democrats in Congress have introduced legislation to ban bump stocks, and President Trump and the influential National Rifle Association have expressed an openness to seeing the devices further regulated.

Analysis | Will Congress ban bump stocks, a gun accessory used in the Las Vegas attack?

Efforts to reach Slide Fire Solutions, based in Moran, Tex., on Tuesday were unsuccessful. In an interview last year with Ammoland.com, a shooting news website, President Jeremiah Cottle, who invented the device, said it was geared toward people who “love full auto” and either cannot afford such a weapon or do not want to fill out the necessary paperwork. The company also has indicated that the device is for people with limited hand mobility, according to federal regulators.

Fully automatic weapons have been heavily restricted in the United States since the enactment of the National Firearms Act more than 80 years ago. In 2010, however, the Bureau of Alcohol, Tobacco and Firearms found that the device isn’t regulated under that law because it is a “firearm part” and not a firearm; bump stocks can replace standard rifle stocks, and owners can easily add or remove them. The suit alleges that the device was intended to circumvent the law.