These laws prohibit the purchase of high-capacity magazines, which are ammunition-feeding devices designed for lethality—enabling a shooter to fire more rounds without pausing to reload. States have typically defined high-capacity to include magazines that hold more than 10 rounds, though a few states provide different thresholds. A full discussion on High Capacity Magazines is here.
The Impact
From 2009 to 2022, the 10 mass shooting incidents with the most casualties all involved the use of at least one firearm equipped with a high-capacity magazine. Research shows that states with restrictions on magazine size experience mass shootings at less than half the rate of states without restrictions.
Source: Cal. Penal Code §§ 32310, 16350, 16740; C.R.S. § 18-12-302(1); Conn. Gen. Stat. § 53-202w(a)-(c); Del. Code Ann. tit. 11, §§ 1465, 1466; Haw. Rev. Stat. § 134-8(c); Md. Code Ann., Crim. Law § 4-305(b); Mass. Gen. Laws ch. 140, §§ 131M, 121; N.J. Stat. Ann. §§ 2C:39-3(j), 2C:39-1(y); N.Y. Penal Law §§ 265.10(1)-(3), (6), 265.36, 265.00(23); R.I. Gen. Laws. §§ 11-47.1-2, 11-47.1-3; 13 V.S.A. § 4021(a); 2021 WA S 5078 (to be codified); D.C. Code § 7-2506.01(b)).
Top 10: Las Vegas, NV, 471 people shot, 60 fatally; Orlando, FL, 102 people shot, 49 fatally; Aurora, CO, 70 people shot, 12 fatally; Highland Park, IL, 53 shot, 7 fatally; El Paso, TX, 46 people shot, 23 fatally; Fort Hood, TX, 45 people shot, 13 fatally; Sutherland Springs, TX, 45 people shot, 25 fatally; Uvalde, TX, 38 people shot, 21 fatally; San Bernardino, CA, 36 people shot, 14 fatally; and Parkland, FL, 34 people shot, 17 fatally. Everytown for Gun Safety Support Fund, “Mass Shootings in America,” accessed January 5, 2023, https://everytownresearch.org/maps/mass-shootings-in-america/.
<1/2: Louis Klarevas, Andrew Conner, and David Hemenway, “The Effect of Large-Capacity Magazine Bans on High-Fatality Mass Shootings, 1990–2017,” American Journal of Public Health 109, no. 12 (2019): 1754-61, https://doi.org/10.2105/AJPH.2019.305311. Study defined mass shooting as six or more shot and killed, excluding the shooter; Sam Petulla, “Here Is 1 Correlation between State Gun Laws and Mass Shootings,” CNN, October 5, 2017, https://cnn.it/2J4sWCC. Study defines mass shootings as incidents where three or more victims, not including the shooter, are shot and killed or shot and wounded.