From the New York Times Upshot news section:
The Mass Shootings Where Stricter Gun Laws Might Have Made a Difference
By Quoctrung Bui, Alicia Parlapiano and Margot Sanger-Katz, June 4, 2022
If the key gun control proposals now being considered in Congress had been law since 1999, four gunmen younger than 21 would have been blocked from legally buying the rifles they used in mass shootings.
At least four other assailants would have been subject to a required background check, instead of slipping through a loophole. Ten might have been unable to steal their weapons because of efforts to require or encourage safer gun storage. And 20 might not have been allowed to legally purchase the large-capacity magazines that they used to upgrade their guns, helping them kill, on average, 16 people each.
Taken together, those four measures might have changed the course of at least 35 mass shootings — a third of such episodes in the United States since the massacre at Columbine High School in Colorado, a New York Times analysis has found. Those 35 shootings killed a combined 446 people.
So, if through some miracle, all 35 mass shootings that might have been affected in some way had been utterly deterred by these four laws, 446 lives would have been saved from 1999 to today. The CDC reports there were 396,762 deaths by homicide from 1999 to 2020, so about 425,000 over the same 1999-2022 period as the NYT’s study, so the maximum imaginable of 446 would be 0.11% of American homicides since 1999.
But another question is how deterrable obsessive, notoriety-seeking kamikaze killers are.
If these proposed laws were, say, 50% effective at preventing murders, that would be 223 lives saved, or about ten per year compared to the 19,141 homicide deaths in 2019 and the 24,576 homicide deaths in 2020. (I know I’m a crazed extremist, but it would seem like a higher priority would be policies to reduce the 5,435 incremental homicides in the year of George Floyd’s death compared to 2019.)
But, saving 10 lives per year would not be an unworthy accomplishment.
And some of these laws might reduce non-glamorous shootings, but who cares about those?