Firearm Type and Number of People Killed in Publicly Targeted Fatal Mass Shooting Events
Leslie M. Barnard, Erin Wright-Kelly, Ashley Brooks-Russell, Marian E. Betz

TL;DR
This study investigates whether assault weapons lead to more deaths in mass shootings in the US.
Contribution
The study empirically evaluates the association between firearm type and casualties in mass shootings.
Findings
Assault weapons are linked to higher numbers of people killed in mass shootings.
The study provides data-driven insights into firearm impact on mass shooting outcomes.
Abstract
This cohort study examines mass shootings in the US to evaluate if assault weapons were associated with a higher number of injuries and deaths.
Genes, proteins, chemicals, diseases, species, mutations and cell lines named across the full text — each resolved to its canonical identifier and authoritative record.
| Characteristic | Total mass shootings, No. (%) (N = 184)a | Incidents where an assault weapon was present, No. (%) (n = 55) | Incidents where an assault weapon was not present, No. (%) (n = 129) | |
|---|---|---|---|---|
| Firearm characteristics | ||||
| Type of firearmc | ||||
| Assault weapon | 55 (29.9) | 55 (100) | NA | NA |
| Handgun | 145 (78.8) | 40 (72.7) | 105 (81.4) | |
| Shotgun | 39 (21.2) | 13 (23.6) | 26 (20.2) | |
| Rifle | 35 (19.0) | 8 (14.5) | 27 (20.9) | |
| No. of firearms present | ||||
| 1 | 88 (47.8) | 10 (18.2) | 78 (60.5) | <.001 |
| 2-4 | 86 (46.7) | 38 (69.1) | 48 (37.2) | |
| ≥5 | 10 (5.4) | 7 (12.7) | 3 (2.3) | |
| Shooter characteristics | ||||
| Age, mean (SD), y | 34.1 (12.6) | 32.8 (12.4) | 34.8 (12.7) | .87 |
| Sex | ||||
| Male | 179 (97.3) | 52 (94.6) | 127 (98.5) | .19 |
| Female | 3 (1.6) | 1 (1.8) | 2 (1.6) | |
| Other | 2 (1.0) | 2 (2.6) | 0 (0.0) | |
| Shooter had an existing relationship with the shooting site | 82 (44.6) | 24 (43.6) | 58 (45.0) | .87 |
| Firearm proficiency | ||||
| No experience | 44 (24.2) | 6 (11.1) | 38 (29.7) | .002 |
| Some experience | 56 (30.8) | 18 (33.3) | 38 (29.7) | |
| More experience | 27 (14.8) | 15 (27.8) | 12 (9.4) | |
| Very experienced | 55 (30.2) | 15 (27.8) | 31 (31.3) | |
| Event morbidity and mortality | ||||
| No. killed, median (IQR) | 5 (4-7) | 6 (5-10) | 5 (4-7) | <.001 |
| No. nonfatally injured, median (IQR) | 3 (1-7) | 6 (2-18) | 2 (1-5) | <.001 |
| Variable | Estimate (95% CI) | |
|---|---|---|
|
| ||
| Crude | 0.65 (0.54-0.78) | <.001 |
| Adjustedb | 0.72 (0.59-0.86) | <.001 |
|
| ||
| Crude | 0.18 (0.12-0.29) | <.001 |
| Adjustedb | 0.27 (0.16-0.44) | .001 |
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Taxonomy
TopicsGun Ownership and Violence Research · Traumatic Ocular and Foreign Body Injuries · Suicide and Self-Harm Studies
Introduction
Mass shootings (MS) account for less than 1% of firearm deaths in the US, but the frequency has increased.^1^ Risk factors for MS perpetration include societal discrimination, contagion effects, firearm access, mental illness, and substance abuse.^2^ Previous geographically and analytically limited studies found MS with handguns had higher fatality rates than those with rifles,^3^ and following an age-based assault weapons (AWs) restriction there was a reduction in firearm violence from AWs.^4^ Another study found that the 1994 federal AWs ban was associated with fewer MS.^5^ To further investigate the association between type of firearm and lethality of MS, this study examined what firearms were present at publicly targeted fatal MS and determined if AWs were associated with a higher number of injuries or deaths.
Methods
The retrospective cohort study was approved by the Colorado Multiple Institutional Review Board and used the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline. Data and definitions came from the Violence Project (eTable in Supplement 1). This study compared publicly targeted fatal MS (ie, an incident where more than 4 people are killed not including the shooter[s], in a public location, not attributable to any other crime) where an AW (any semiautomatic gun that can accept a detachable ammunition magazine that has 1 or more additional features considered useful in military applications) was present vs not by shooter and event characteristics. We used negative-binomial regression to model associations between firearm type and the number killed and the number nonfatally injured. Confounders (multiple firearms, firearm proficiency, familiarity with location, shooter age, and shooter sex) were identified a priori based on theory and empirical evidence.^2^ This analysis was limited to single shooter events. Significance was set at P < .05, and tests were 2-sided. Data were analyzed from August 1, 1966, to November 6, 2023, using SAS software version 9.4 (SAS Institute). Additional information can be found in the eMethods in Supplement 1.
Results
From August 1, 1966, to November 6, 2023, there were 184 publicly targeted fatal MS (3.2 per year) with 1342 total deaths and 2084 nonfatal injuries. Multiple firearms were present in 96 events (52.2%) (mean 3.1 per event); handguns were the most common firearm type (145 MS [78.8%] involved a handgun) followed by 55 (29.2%) that involved an AW, but only 13 (7.1%) involved AWs exclusively. Incidents with AWs (vs without) were more likely to have multiple firearms (45 [81.8%] vs 51 [39.5%]) and shooters with no firearms experience (6 [11.1%] vs 38 [29.7%]) (Table 1).
Incidents where an AW was present resulted in a mean of 0.72 (95% CI, 0.59-0.86) more people killed when controlling for confounding compared with events without an AW present. Incidents where an AW was present were also associated with the number injured after adjusting for confounding (0.27 [95% CI, 0.16-0.44]) (Table 2).
Discussion
We found most publicly targeted fatal MS involved multiple types of firearms and handguns were the most common type of firearm present. AWs being present during a publicly targeted mass shooting was associated with a slight increase in the number of injuries and deaths occurring during that incident.
There may be opportunities to intervene before a MS. Previous research found that plans to commit MS were disclosed before 47% of MS.^6^ Policies regulating firearm access show promise. Age-based AWs restrictions may be effective in reducing MS.^4^ Moreover, child access prevention laws, which require secure firearm storage to prevent child access, and extreme risk protection orders, which temporarily remove firearms from those who threaten violence, may be effective in preventing MS. Finally, secure storage in-home or out-of-home may be an effective strategy when risk for perpetration exists.
Limitations included the Violence Project definition of MS and AW. We used the type of firearms present as a proxy for use; this may have led to misclassification. Enhanced and systematic data collection is needed on MS in the US including border definitions of MS and the types of firearms used. Understanding contributing factors associated with MS can inform additional research, policies, and interventions.
The reference list from the paper itself. Each links out to its DOI / PubMed record.
- 1Web-based Injury Statistics Query and Reporting System. US Centers for Disease Control and Prevention. Accessed December 27, 2024. https://www.cdc.gov/injury/wisqars/index.html
- 2Silver J, Silva JR. A sequence analysis of the behaviors and experiences of the deadliest public mass shooters. J Interpers Violence. 2022;37(23-24):NP 23468-NP 23494. doi:10.1177/0886260522107881835430903 · doi ↗ · pubmed ↗
- 3Sarani B, Hendrix C, Matecki M, . Wounding patterns based on firearm type in civilian public mass shootings in the United States. J Am Coll Surg. 2019;228(3):228-234. doi:10.1016/j.jamcollsurg.2018.11.01430529633 · doi ↗ · pubmed ↗
- 4Bhullar A, Shipley J, Alaniz L, . Washington state assault weapon firearm violence before and after firearm legislation reform. Am Surg. 2024;90(10):2384-2388. doi:10.1177/0003134824124464438580618 · doi ↗ · pubmed ↗
- 5Di Maggio C, Avraham J, Berry C, . Changes in US mass shooting deaths associated with the 1994-2004 federal assault weapons ban: analysis of open-source data. J Trauma Acute Care Surg. 2019;86(1):11-19. doi:10.1097/TA.000000000000206030188421 · doi ↗ · pubmed ↗
- 6Peterson J, Erickson G, Knapp K, Densley J. Communication of intent to do harm preceding mass public shootings in the United States, 1966 to 2019. JAMA Netw Open. 2021;4(11):e 2133073. doi:10.1001/jamanetworkopen.2021.3307334735012 PMC 8569489 · doi ↗ · pubmed ↗
