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Assault Weapons and High-Capacity Magazines

3.22.2019

Last Updated: 3.18.2022

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Introduction

Assault weapons and high-capacity magazines are commonplace in mass shootings and make shootings more lethal. Research shows that restrictions on assault weapons and high-capacity magazines can help prevent mass shooting injuries and fatalities as well as reduce the devastation of daily gun violence in America.

Background

Assault weapons and high-capacity magazines are exceptionally deadly. High-capacity magazines, commonly defined as ammunition magazines capable of holding more than 10 rounds, allow a shooter to fire more rounds without pausing to reload. The more rounds a shooter can fire consecutively, the more gunshot wounds they can inflict during an attack.1Elzerie de Jager et al., “Lethality of Civilian Active Shooter Incidents With and Without Semiautomatic Rifles in the United States,” JAMA 320, no. 10 (2018): 1034, https://doi.org/10.1001/jama.2018.11009.

Assault weapons are generally high-powered semiautomatic firearms where each round has up to four times the muzzle velocity of a handgun round.2Peter M. Rhee et al., “Gunshot Wounds: A Review of Ballistics, Bullets, Weapons, and Myths,” The Journal of Trauma and Acute Care Surgery 80, no. 6 (June 2016): 853–67, https://doi.org/10.1097/TA.0000000000001037. Generally, most current state laws define assault weapons to include semiautomatic firearms that have a number of military-style features, semiautomatic firearms that come equipped with fixed high-capacity magazines, or other specifically enumerated high-powered firearms. This means that each round from an assault weapon inflicts greater damage to the human body than a round from a typical handgun.3Rhee et al., “Gunshot Wounds.” What’s more, assault weapons are generally designed to fire rounds at a greater rate than other firearms, and when combined with high-capacity magazines, they enable a shooter to fire more rounds over a short period.

Seven states and Washington, D.C. have some type of assault weapons prohibition in place.Nine states and Washington, D.C. have some type of high-capacity magazine prohibition in place.
California
Colorado
Connecticut
Hawaii
Maryland
Massachusetts
New Jersey
New York
Vermont
Washington, D.C.

Key Findings

Assault weapons and high-capacity magazines are frequently used in mass shootings, resulting in more deaths and injuries. Between 2009 and 2020 in the US, the 10 mass shooting incidents with the most casualties all involved the use of a firearm equipped with a high-capacity magazine, an assault weapon, or both (Las Vegas, NV; Orlando, FL; Aurora, CO; El Paso, TX; Fort Hood, TX; Sutherland Springs, TX; San Bernardino, CA; Parkland, FL; Odessa/Midland, TX; and Newtown, CT).4Las Vegas, NV, 471 people shot, 60 fatally; Orlando, FL, 102 people shot, 49 fatally; Aurora, CO, 70 people shot, 12 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; San Bernardino, CA, 36 people shot, 14 fatally; Parkland, FL, 34 people shot, 17 fatally; Odessa/Midland, TX, 32 people shot, 7 fatally; and Newtown, CT, 29 people shot, 27 fatally. Everytown for Gun Safety Support Fund, “Twelve Years of Mass Shootings in the United States,” June 4, 2021, https://everytownresearch.org/maps/mass-shootings-in-america/. This report defines a mass shooting as an incident in which four or more people, not including the shooter, are killed with a firearm. The 2009 Fort Hood, TX, shooter—who shot and killed 13 people and injured 32 more—specifically sought out high-capacity magazines in preparation for his attack. A witness to the shooter’s purchase at a Killeen, TX, gun dealer reported, “He gave me two specifications. He said he wanted the most technologically advanced weapon on the market and the one with the highest magazine capacity.”5Scott Huddleston, “Hasan Sought Gun with ‘High Magazine Capacity,’” My San Antonio, October 21, 2010, https://bit.ly/3sRgG1v. 

A study of mass shooting incidents between 1981 and 2017 found that assault rifles accounted for 86 percent of the 501 fatalities reported in 44 mass shooting incidents.6Charles DiMaggio et al., “Changes in US Mass Shooting Deaths Associated With the 1994-2004 Federal Assault Weapon Ban: Analysis of Open-Source Data,” The Journal of Trauma and Acute Care Surgery 86, no. 1 (2019): 11–19, https://doi.org/10.1097/TA.0000000000002060. Study defines a mass shooting as an incident in which four or more people, not including the shooter, are killed with a firearm. An analysis of Everytown’s Mass Shootings in America database similarly reveals the outsize impact the use of assault weapons and/or high-capacity magazines has on the number of casualties associated with these incidents. Between 2009 and 2020, mass shootings where an assault weapon was used accounted for a quarter of all mass shooting deaths and more than three-quarters of all injuries.7Everytown for Gun Safety Support Fund, “Twelve Years of Mass Shootings in the United States,” June 4, 2021, https://everytownresearch.org/maps/mass-shootings-in-america/. In the 12 years from 2009 to 2020, there were at least 30 mass shootings (16 percent of those with known weapon data) that involved the use of an assault weapon, resulting in 347 deaths and 707 injuries. Shootings where assault weapons were used resulted in nearly six times as many people shot, more than twice as many people killed, and nearly 22 times as many people wounded per incident on average.8Everytown for Gun Safety Support Fund, “Twelve Years of Mass Shootings in the United States.” The 30 mass shootings involving assault weapons resulted in an average of 35.1 people shot, 11.6 people killed and 23.6 people wounded per incident, compared to an average of 5.9 people shot, 4.8 people killed and 1.1 people wounded when other or unknown-type guns were used. Incidents involving a firearm equipped with a high-capacity magazine resulted in nearly five times as many people shot, more than twice as many fatalities, and nearly 14 times as many injuries per incident on average compared to those that did not involve the use of high-capacity magazines.9Everytown for Gun Safety Support Fund, “Twelve Years of Mass Shootings in the United States.” The 42 incidents involving the use of high-capacity magazines resulted in 26.7 people shot, 10.0 people killed and 16.6 people wounded on average per incident, compared to an average of 5.9 people shot, 4.8 people killed and 1.2 people wounded on average that resulted from the 198 incidents that did not involve the use of high-capacity magazines or magazine capacity was undetermined.

Assault weapons led to 6x as many people shot per mass shooting

Last updated: 3.18.2022

High-capacity magazines led to 5x as many people shot per mass shooting

Last updated: 3.18.2022

Assault weapons and high-capacity magazines are frequently used in the crimes that plague our nation. A 2018 study estimated that firearms equipped with high-capacity magazines, which include assault weapons as well as other high-capacity semiautomatic firearms, account for 22 to 36 percent of crime guns in most places, with some estimates upwards of 40 percent for cases involving serious violence, including homicides of law enforcement officers. The problem may be getting worse: research suggests the prevalence of high-capacity magazines in guns used in crimes has grown substantially since the 2004 expiration of the federal prohibition on assault weapons and high-capacity magazines.10Christopher S. Koper et al., “Criminal Use of Assault Weapons and High-Capacity Semiautomatic Firearms: An Updated Examination of Local and National Sources,” Journal of Urban Health 95, no. 3 (2018): 313–21, https://doi.org/10.1007/s11524-017-0205-7.

Evidence

A growing body of research shows that states can reduce gun violence by prohibiting assault weapons and high-capacity magazines. States with restrictions on magazine size experience mass shootings at less than half the rate of states without restrictions.11Sam 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 injured with a firearm. According to Dr. Michael Siegel, a researcher at Boston University, “Whether a state has a large capacity ammunition magazine ban is the single best predictor of the mass shooting rates in that state.”12Petulla, “Correlation between State Gun Laws and Mass Shootings.”

A 2019 study found that mass shooting fatalities were 70 percent less likely to occur from 1994 to 2004, when the federal prohibition on assault weapons and high-capacity magazines was in effect, than during the 12 years studied before and after the prohibition. Researchers estimate a federal Assault Weapon Ban (AWB) would have prevented 314 of 448 mass shooting deaths that occurred during the studied periods where the AWB was not in effect.13DiMaggio et al., “Federal Assault Weapons Ban.”

In Virginia, the AWB was associated with significant reductions in the share of guns used in crimes that were equipped with high-capacity magazine, down to an all-time low of 10 percent in 2004. When the prohibition expired, the share of Virginia crime guns equipped with high-capacity magazines rapidly increased, reaching 22 percent by 2010.14David S. Fallis and James V. Grimaldi, “Va. Data Show Drop in Criminal Firepower during Assault Gun Ban,” Washington Post, January 22, 2011, https://wapo.st/3Cugf0g.

Everytown Research & Policy is a program of Everytown for Gun Safety Support Fund, an independent, non-partisan organization dedicated to understanding and reducing gun violence. Everytown Research & Policy works to do so by conducting methodologically rigorous research, supporting evidence-based policies, and communicating this knowledge to the American public.

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