Joe Biden said mass shootings tripled when the assault weapon ban ended. They did

There was no mistaking President Joe Biden’s plea for some sort of concrete response to the slaying of 19 elementary school children and two teachers in Uvalde, Texas.

"I spent my career as a senator and as vice president working to pass common sense gun laws," Biden said in a May 24 prime time national address. "We can’t and won’t prevent every tragedy. But we know they work and have a positive impact. When we passed the assault weapons ban, mass shootings went down. When the law expired, mass shootings tripled."

Biden was thinking back to sweeping gun legislation passed in 1994. Among other changes, it banned certain kinds of weapons, and the large-capacity magazines that allow people to fire more bullets before reloading.

There are numbers that back Biden up. A 2019 study out of New York University’s School of Medicine found that mass shooting deaths involving assault weapons fell slightly in the decade of the federal assault weapon ban, and then rose dramatically in the decade that followed. That’s the time frame for Biden’s statement.

While other researchers said the decline during the ban was too small to draw firm conclusions about the ban’s impact, there is no debate that the pace and deadliness of mass shootings rose after the ban ended. Beyond assault weapons, more recent work points to the threat posed by large-capacity magazines, which the 1994 law also restricted.

The 1994 law barred the "manufacture, transfer, and possession" of about 118 firearm models and all magazines holding more than 10 rounds. People who already owned such weaponry could keep it. When the ban took effect, there were roughly 1.5 million assault weapons in private hands. An estimated 25 million weapons were equipped with large-capacity magazines.

The ban expired in 2004.

In a 2004 study commissioned by the U.S. Justice Department, researcher Christopher Koper wrote, "The ban’s exemption of millions of pre-ban assault weapons and large capacity magazines ensured that the effects of the law would occur only gradually."

The point was the 1994 law was hardly an on-off switch for these firearms and magazines. As long as that hardware remained in circulation, people who wanted to use these weapons in a mass shooting would have some opportunity to acquire them.

In a 2019 study from New York University’s School of Medicine, a group led by epidemiologist Charles DiMaggio homed in on mass shooting deaths.

Researchers define mass shootings in different ways. DiMaggio’s group looked at incidents in which at least four people died.

In raw numbers, they found that mass shooting deaths fell during the years of the ban, and rose afterwards. DiMaggio shared his data. Deaths more than tripled in the decade after the ban ended.

The decline of 15 deaths between the decade before the ban and the decade during it is modest, but there is a clear and dramatic rise after the ban expired. 

The death toll from mass shootings went from an average of 4.8 per year during the ban years to an average of  23.8 per year in the decade afterwards.

Many factors drive gun deaths. To help account for those, DiMaggio’s team put mass shooting deaths in terms of the total number of firearm homicides. Viewed that way, they found that between 1994 and 2004, the yearly rate fell by 9 people per 10,000 firearm homicides. 

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DiMaggio’s study concluded that mass shooting deaths were 70% less likely during the ban. 

His isn’t the only study to find that fewer people died in mass shootings when the ban was in effect. In a 2019 article, Louis Klarevas, a Columbia University researcher, and his co-authors found that shootings in which six or more people died were less common and less deadly in the years during the ban.

The debate over the value of a ban on assault weapons and large-capacity magazines often includes Christopher Koper at George Mason University. Koper wrote the 2004 study that gave both sides in the gun control debate supporting material.

Recently, Koper has spent more time assessing the role of large-capacity magazines that hold more than 10 rounds. 

In a 2020 article, Koper wrote that more than the semiautomatic weapons themselves, the latest data ties larger magazines to a rising death toll. The most striking trend, he said, is less about the modest fall in deaths under the ban, and more about the dramatic rise that came when the ban ended.

Much of that stems from the firepower that comes from large-capacity magazines.

"Considering that mass shootings with high capacity semiautomatics are considerably more lethal and injurious than other mass shootings, it is reasonable to argue that the federal ban could have prevented some of the recent increase in persons killed and injured in mass shootings had it remained in place," Koper wrote.

Researchers at the Johns Hopkins School of Public Health studied state laws that limit magazine size. Their work linked those laws to a nearly 50% reduction in the rate of fatal mass shootings.

On the key policy question of whether the ban drove the decline, DiMaggio urged caution.

"It is pretty much impossible to prove cause and effect," he told us when his study came out in 2019.

Gun violence researcher Andrew Morral at RAND Corporation, a consulting nonprofit research group, said he and his colleagues don’t see strong evidence that the ban drove down deaths. 

On the other hand, "we also don’t believe there is strong evidence that they were not the cause of any such reductions," Morral said.

Morral said many studies show that limits on weapons and large-capacity magazines are associated with fewer and less deadly mass shootings. And in the absence of stronger data either way, "logical considerations" should guide lawmakers.

"The absence of strong scientific evidence is not a good rationale for taking no action," Morral said.

Biden said that after passage of "the assault weapons ban, mass shootings went down. When the law expired, mass shootings tripled."

We last looked at a claim like this in 2019, when Bill Clinton said that after the ban on some types of assault weapons passed, "there was a big drop in mass shooting deaths." Biden didn’t go that far, and as such, is a bit more accurate. 

A key study backs Biden up. But the reality is millions of assault weapons and large-capacity magazines remained in circulation during the ban, and that makes it hard to tease out the law’s impact. 

We rate this claim Mostly True.