Ezra examines the evidence:
Did the law have an effect on mass shootings? That’s possible. As this chart from Princeton’s Sam Wang shows, the number of people killed by mass shootings did go down in the years the ban was in effect (save for a surge in 1999, a year that included Columbine) … Because mass shootings are relatively rare, it’s difficult to tell whether this is just random variation or whether the assault weapons ban actually had an impact. Still, the number of mass shootings per year has doubled since the ban expired. That’s suggestive, at least.