Assessing the potential to reduce deaths and injuries from mass shootings through restrictions on assault weapons and other high‐capacity semiautomatic firearms

• DOI: http://doi.org/10.1111/1745-9133.12485
• Published date: 01 February 2020
• Author: Christopher S. Koper
• Date: 01 February 2020

DOI: 10.1111/1745-9133.12485

SPECIAL ISSUE ARTICLE

COUNTERING MASS VIOLENCE IN THE UNITED STATES

Assessing the potential to reduce deaths and injuries

from mass shootings through restrictions on assault

weapons and other high-capacity semiautomatic

firearms

Christopher S. Koper

George Mason University

Correspondence

Christopher S. Koper,Department of Cr iminol-

ogy,Law & Society,Center for Evidence-Based

Crime Policy,George Mason University,4400

UniversityDrive, MS 6D12, Fairfax, VA22030.

Email:ckoper2@gmu.edu

Theaut hor thanks WilliamJohnson for research

assistancein t he preparation of this paper.An

earlierversion of this paper was presented at

the GeorgeMason University-Carnegie Mellon

UniversityWorkshop on An Evidence-Based

Approachto Understanding and Counter-

ingMass Violence in America held in Apr il

2019wit h funding fromt he NationalScience

Foundation.The aut hor thanks conference

participants fortheir comments on t he earlier

draft.

Research Summary: This article examines the use,

impacts, and regulation of assault weapons and other

high-capacity semiautomatic firearms as they pertain to

the problem of mass shootings in the United States. High-

capacity semiautomatics (which include assault weapons

as a subset) are used in between 20% and 58% of all firearm

mass murders, and they are used in a particularly high

share of public mass shootings. Mass shootings perpetrated

with these firearms result in substantially more fatalities

and injuries than do attacks with other firearms, and these

differences are especially pronounced for the number of

victims with nonfatal gunshot injuries. The federal ban on

assault weapons and large-capacity (>10 rounds) ammuni-

tion magazines of 1994 had exemptions and loopholes that

limited its short-term effects, but its expiration in 2004 was

followed byan increase in the use of t hese weaponsin mass

shootings and other crimes. Growing evidence suggests

that state-level restrictions on large-capacity magazines

reduce mass shootings, but further research is needed on

the implementation and effects of these laws.

Policy Implications: Restrictions on large-capacity maga-

zines are the most important provisions of assault weapons

laws in part because they can produce broader reductions

in the overall use of high-capacity semiautomatics that

facilitate high-volume gunfire attacks. Data on mass

shooting incidents suggest these magazine restrictions can

Criminology & Public Policy. 2020;19:147–170. wileyonlinelibrary.com/journal/capp © 2020 American Society of Criminology 147

148 KOPER

potentially reduce mass shooting deaths by 11% to 15% and

total victims shot in these incidents by one quarter, likely

as upper bounds. It may take several years for the effects of

these laws to be fully realized, however, depending on their

specific provisions, especially with regard to treatment of

pre-ban weaponry.

Dating back to the 1980s, public concern over mass shootings in the United States has prompted ongo-

ing debates about the need to restrict particularly deadly categories of firearms that can facilitate the

commission of such acts. These debates have focused broadly on semiautomatic firearms with large

ammunition capacities and more specifically on subsets of these firearms, known as “assault weapons,”

with additional military-style features that are believed to make them more dangerous and/or attrac-

tive for criminal uses. Over the last several decades, these types of firearms have been used in many

of the most deadly and injurious acts of mass violence in the United States. In response, the fed-

eral government imposed restrictions on these weapons in 1994 but allowed them to expire in 2004.

Debates about reinstating these restrictions have intensified during the last fewyears mainly in response

to several recent and highly tragic public mass shootings perpetrated with assault weapons or other

high-capacity semiautomatics. Although efforts to revive the federal restrictions havebeen unsuccess-

ful to date, nine states and the District of Columbia currently have their own restrictions on such

weapons, as do some additional localities (see the Giffords Law Center to Prevent Gun Violence at

https://lawcenter.giffords.org/).

In this essay, I examine available data on the use of assault weapons and other high-capacity semi-

automatics in mass shootings and investigate the potential to reduce deaths and injuries from mass

violence through restrictions on these weapons. I also examine whether federal and state restrictions

on these weapons have been effective in reducing their use in mass shootings. In summary, available

evidence, while limited in quantity and precision, suggests that restrictions on these weapons have the

potential to reduce deaths and injuries from mass shootings, at least modestly and perhaps by more

substantial margins, especially for nonfatal injuries. Despite the limitations of the prior federal law

restricting these weapons, its expiration has coincided with a rise in crimes with high-capacity semiau-

tomatics that has likely contributed to higher victim counts in mass shootings. The effects of state-level

restrictions, which vary in important ways, are not yet clear, even though there is growing evidence

that states with these restrictions have fewermass shootings. Having noted these tentative conclusions,

there is need for better data and more in-depth research on various aspects of this issue.

1OVERVIEW ON THE AVAILABILITY, USE, AND

RESTRICTION OF ASSAULT WEAPONS AND OTHER

HIGH-CAPACITY SEMIAUTOMATICS

Laws aimed at curbing the availability and use of semiautomatic assault weapons (AWs) and other

high-capacity semiautomatics focus on two categories of weaponry.1AW laws impose restrictions on

semiautomatic firearms that accept detachable ammunition magazines and have one or more additional

military-style features that are considered useful in military and criminal applications but unnecessary

in shooting sports or self-defense. Examples of the latter features include pistol grips on rifles, flash

hiders, folding rifle stocks, threaded barrels for attaching silencers, and barrel shrouds on pistols.2