States and municipalities nationwide are attempting to ban bump stocks -- devices used to make rifles fire more rapidly -- after Congress failed to act on bipartisan resolve to restrict them following their use in a Las Vegas massacre last year.

At least 15 states are considering laws that would ban bump stocks, as is Denver. Columbia, S.C., barred them last year. The devices already are illegal in California, and some other states with bump stock restrictions are trying to tighten them.

They include New Jersey, where, in one of his last acts in office, former Gov. Chris Christie (R) on Monday completely barred bump stocks from the state. Though the use of bump stocks already had been illegal in New Jersey, the new law prohibits possessing or selling them. Owners have 90 days to voluntarily surrender their bump stocks to law enforcement, and retailers must turn them in within 30 days.

A bump stock is a molded piece of plastic or metal that gun owners can affix to their firearms, effectively allowing semi-automatic firearms to behave like fully automatic rifles, with a higher firing rate. Once known only among gun enthusiasts, the add-on devices gained widespread attention in October, after Stephen Paddock used them to fire bullets from a 32nd floor suite at the Mandalay Bay resort in Las Vegas onto a country music festival below. Fifty-eight people died and about 500 were treated for injuries in what was the worst mass shooting in modern U.S. history.

A bipartisan coalition in Congress and the National Rifle Association almost immediately said the devices should be subject to additional regulations. Republican lawmakers punted to the Bureau of Alcohol, Tobacco, Firearms and Explosives, which has said it cannot regulate bump stocks unless Congress changes the law; the question is currently under administrative review. Bills were proposed in the Senate and House to completely ban bump stocks but no action was taken and the NRA opposes them.

In lieu of federal restrictions, states are acting to bar bump stocks and conversion kits that similarly allow semi-automatic weapons to fire much like an automatic weapon would.

“The states are actually really leading the way, and they are the true leaders on this issue while Congress continues to not act to ban these devices,” said Robin Lloyd, government affairs director for Giffords, the gun-control group.

Massachusetts was the first state to ban bump stocks in the wake of the Las Vegas shooting, with Lt. Gov. Karyn Polito (R) signing a bill in November. Gov. Charlie Baker was out of the state at the time.

“Governor Baker and Lt. Governor Polito support the Second Amendment to the Constitution and Massachusetts’ strict gun laws, including the ban on assault weapons and bump stocks, and are pleased that the Commonwealth continues to lead in passing commonsense reforms,” Brendan Moss, a spokesman for Baker, said in a statement.

Groups such as Giffords and Everytown for Gun Safety are increasingly focusing on states when it comes to gun-control measures. John Feinblatt, president of Everytown, said he believes gun-related issues such as bump stocks are less politically charged at the state level.

But pro-gun groups steadfastly oppose such legislation and believe some of the new state laws might be challenged in court.

Theresa Inacker, communications director for the Coalition of New Jersey Firearm Owners, said the state’s ban on bump stocks doesn’t affect many legal gun owners there because they already were barred from using them. But she fears it could open the door to further state restrictions, including on the number of rounds allowed in a magazine, and is leery of the state taking legally purchased items away from residents.

“The confiscation part of it is disconcerting,” she said. “We have to ask ourselves the questions, ‘How is that American? How is that just, or when does it end?’”

Both proponents and opponents of bump stocks are now testifying in state legislatures. Zach Elmore, 31, of Seattle, drove an hour to Olympia, the state capital, on Monday to tell lawmakers that bump stocks should be banned in Washington state. Elmore’s sister, Alicia Johnson, was wounded in the Las Vegas shooting.

Elmore did his best to tell his sister’s story in two minutes: She and her husband didn’t know there was a shooting until they saw a man standing next to them shot and killed. They hid behind a barrier and, on a second attempt at escaping, Johnson was shot in the back. She crumpled to the ground, texted her family what she thought were goodbye messages and was thrown into a truck filled with bodies heading for a hospital.

Elmore said his sister is physically doing well, but she struggles with survivor’s guilt and “She’s not as okay as she thinks she is.”

The shooting was the “breaking point” for him, and he decided to get involved in gun control.

“I really just kind of wanted to express what it’s like as a family to go through that and why it might be important to ban bump stocks or conversion kits,” he said. “I kind of find that hard to believe that the average Joe need access to one of those.”