While gun violence declined last year, a closer look at the data reveals a striking and surprising trend. While the total number of shootings is going down, the lethality of shootings — the odds of someone dying in a shooting — seems to be going up. If that trend holds, it could have massive consequences for gun violence in America, with hundreds or thousands more homicides per year.

A few years ago at a Chicago police station, one of us saw why this is happening. Officers who had stopped some teenagers in a car dropped on a desk what they had found during that stop: a semi-automatic pistol with a giant drum magazine appended to the bottom, which would allow the user to fire 100 rounds before reloading. That kind of alteration seems to be more common across the country and is leading to shootings becoming more deadly.

We can see the tragedies that result from data from Chicago over the past 13 years.

The number of high-capacity magazines, holding 15 or more rounds, that police recover on the streets has increased sixfold. That trend is interacting in an unhelpful way with the development of so-called Glock switches. One of the most effective gun laws in federal history came from President Franklin D. Roosevelt’s efforts in the 1930s to ban machine guns. What’s left on the market are semi-automatic firearms that fire once every time the trigger is pulled.

Glock switches are post-market devices that convert these guns into automatic firearms; that is, anyone with $50 and an internet connection can turn a regular semi-automatic firearm into a machine gun. While these were unheard of in 2010, last year, Chicago police seized 447 guns modified to fire fully automatically. From a public safety perspective, it’s not ideal for someone to be able to fire 100 rounds without having to reload; it’s even less ideal for those 100 rounds to be fired at a machine gun rate.

More high-capacity magazines and Glock switches have led the number of shell casings recovered at each shooting to surge. The number of shooting scenes in which police recovered 20 or more casings increased from 23 in 2010, less than 1% of total shooting incidents, to 386 last year — or nearly 16% of total shooting incidents.

Why is this such a big problem? The more rounds fired in each shooting, the higher the chances someone is hit — in particular, multiple times.

That’s reflected in a rising shooting fatality rate, from 1 in 7 (12.6%) to closer to 1 in 5 today (18.7%). With 2,000 to 3,000 shootings per year in Chicago, seemingly small differences in lethality can have a large impact on total homicides. In 2023, the city had 184 more fatal shootings than it would have had if lethality had not increased. That’s equal to about one-third of the total homicides in Chicago last year. That’s 184 families devastated by the loss of a mother, brother, father, son or daughter, families that now will never be the same.

This isn’t limited to Chicago. Data from Philadelphia and Los Angeles show that shooting lethality has increased in those cities as well. If the fatality rate hadn’t increased in Los Angeles, that city would have had 49 fewer homicides last year. Philadelphia would have had 69 fewer homicides.

This trend has a little bit of a “back to the future” flavor. Thirty years ago, the federal government banned high-capacity magazines that held 10 or more rounds. But that ban was allowed to sunset. We’re seeing the consequences play out across the country, particularly in our most economically disadvantaged urban neighborhoods.

Amid America’s heated debate over gun control, survey data suggests high-capacity magazines might be an area of reasonably bipartisan consensus: Most Americans agree you don’t need a 100-round magazine and a Glock switch to hunt or protect your home against an invader. Yet these are having devastating consequences for public health.

Glock switches and high-capacity magazines may be low-hanging fruit for legislators. Targeting them potentially could save a remarkable number of lives in short order.

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Jens Ludwig is the Edwin A. and Betty L. Bergman distinguished service professor at the University of Chicago and Pritzker director of the University of Chicago Crime Lab. Jacob Miller is an analyst at the University of Chicago Crime Lab.

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