These nine states prohibit the purchase and possession (or in the case of Washington, the sale and manufacture) of assault weapons — high-powered semi-automatic firearms including AR-15 and AK-47 rifles that are used in most high-profile mass shootings. In addition to these states, Hawaii prohibits assault pistols but its law does not cover assault-style rifles. While state definitions vary, assault weapons typically fire rounds with up to four times the muzzle velocity of a standard handgun round—inflicting greater damage on the human body. A full discussion on Assault Weapons is here.
From 2009 to 2022, nine out of the 10 mass shooting incidents with the most casualties involved the use of at least one assault weapon. A 2021 study found that the federal prohibition on assault weapons and high-capacity magazines was associated with a significant decrease in public mass shootings and related casualties, and prevented at least 11 public mass shootings during the 10 years it was in effect. The researchers also estimated that had the law remained in effect from 2005 through 2019, it would have prevented 30 mass shootings that killed 339 people and wounded 1,139 more.
