An assault weapons ban might not end mass shootings. But it would help.

Law enforcement officers respond to an active shooter at the Old National Bank building on April 10, 2023, in Louisville, Kentucky. | Luke Sharrett/Getty Images

Biden has called for an assault weapons ban after recent mass shootings. Why hasn’t Congress acted?

The gunman who killed at least five people and injured eight more in Monday’s mass shooting at a bank in Louisville, Kentucky, was reportedly armed with an AR-15-style semi-automatic rifle, which is designed to kill efficiently without having to reload frequently and is therefore considered an assault weapon.

Such assault weapons, which are usually used alongside high-capacity magazines, are common in mass shootings: They have been used in over half of the deadliest mass shootings since 1966 and account for 38 percent of the deaths in mass shootings in that period, according to the Violence Project.

That has led President Joe Biden to repeatedly push for a national assault weapons ban, most recently after another recent shooting at Covenant School in Nashville, Tennessee.

The US has had a national assault weapons ban before. As a senator, Biden helped pass the last national ban in 1994; it expired when lawmakers failed to renew it in 2004. Following a school shooting in Uvalde, Texas, last year, Congress passed its first gun reforms in decades encouraging states to pass red flag laws, implementing enhanced background checks for gun buyers under 21, and closing the “boyfriend loophole” which allowed some people with domestic violence convictions to purchase guns.

But that package didn’t include an assault weapons ban. That’s despite the fact that most Americans, including 86 percent of Democrats and 47 percent of Republicans, support such a ban, according to a June 2022 survey by Morning Consult. Now that Republicans — who continue to oppose any kind of perceived infringement on gun rights — control the House, the likelihood that Congress could pass such a ban in the near future remains slim.

Why the US doesn’t have a national assault weapons ban

National efforts to ban assault weapons have repeatedly failed in recent years. The 1994 ban also included a prohibition on high-capacity magazines, which most Americans would support renewing, according to the Pew survey. But as with banning assault weapons, there’s a big partisan split: 88 percent of Democrats and 51 percent of Republicans are in favor, according to the Morning Consult survey.

Since the law expired, there has been a sharp increase in the number of mass shooting casualties due to assault weapons. One 2019 study found that mass shooting deaths were 70 percent less likely to occur while the federal assault weapons ban was in effect based on data from 1981 to 2017.

“We’re seeing more of them because there are more of them and they’re easier than ever to get. And there is an appeal to those who wish to do harm to the community,” said Nick Suplina, senior vice president of law and policy at the advocacy group Everytown for Gun Safety.

In lieu of a federal ban, nine states, along with Washington, DC, have implemented their own assault weapons bans — but Kentucky is not among them. Rather, the state has taken steps to loosen its gun laws in recent years: In 2019, the state legislature passed a law that allows most adults 21 or older to carry firearms without a permit. The Kentucky legislature has also passed a law that shields the state from any federal firearm ban.

Illinois became the latest state to ban assault weapons in January. Washington is also set to enact a ban once Democratic Gov. Jay Inslee signs it. Colorado Democrats have also introduced a similar measure, but the issue has proved divisive in the caucus.

Do assault weapons bans work?

Mass shootings are difficult to study because they are uncommon occurrences, though more common in the US than in other countries. So that makes it hard to understand how gun policies, including assault weapons bans, might impact both the number of mass shooting incidents and the number of casualties.

The RAND Corporation, for instance, conducted a review of six studies on the effects of state or federal assault weapons bans on multiple-victim shootings and found the results inconclusive.

But individual studies have found evidence that assault weapons bans are effective. A 2021 study found that had the federal assault weapons ban remained in effect from 2005 through 2019, it would have prevented 30 mass shootings where an assault weapon was obtained legally resulting in the deaths of 339 people.

Beyond assault weapons bans, there are policies that evidence suggests might be more effective at preventing mass shootings and gun violence overall. For instance, extreme risk protection laws, otherwise known as “red flag” laws, can bar individuals who are believed to pose a danger to themselves or others from possessing firearms. These laws have increasingly come into favor in part because assault weapons account for only a small percentage of firearm murders overall.

“These laws are newer than assault weapons bans, but there’s already a really strong and growing body of evidence that shows that they’re very effective at preventing mass shootings, but even more so at preventing suicides,” said David Pucino, Giffords Law Center’s deputy chief counsel.

But that’s not to say that assault weapons bans shouldn’t be on the table.

“Everything that we know about mass shootings suggests that assault weapons, especially when equipped with high-capacity magazines, make them more deadly,” Suplina said. “If something is legally and commonly available, you’re only increasing the likelihood that it will be misused and or fall into the hands of somebody who is prohibited from possessing them.”

Update, April 11, 11:30 am ET: This story was originally published on March 28 and has been updated with information on the Louisville shooting.