Guns Used in School Shootings: Types, Sources, and Liability

Handguns are the guns most often used in school shootings in the United States, appearing in roughly 86 percent of incidents carried out by adolescents, according to a study in JAMA Pediatrics that examined 253 school shootings between 1990 and 2016.¹ Rifles were used in about 9 percent of cases, shotguns in about 6 percent.² Those proportions flip when you look at the deadliest attacks. The school shootings with the highest body counts of the past fifteen years have almost all involved AR-15-style semiautomatic rifles, and where the shooter was under 18, the gun almost always came from a relative’s home.

What Guns Show Up Most Often

The JAMA Pediatrics data breaks down further by caliber and mechanism. Among identified firearms used by adolescent shooters, .22 was the most common caliber at 26.9 percent, followed by 9 mm at 5.6 percent. About 59 percent of the guns were semiautomatic or fully automatic, and most were classified as lower or moderate in power. The researchers found a “stability in the use of high-powered weapons” across the study period: handguns dominated throughout, and the share of higher-powered firearms did not decline.¹

The pattern holds in the broader mass-shooting data. Drawing on The Violence Project database of 172 mass shooters from 1966 to 2019, the National Institute of Justice found handguns involved in 77 percent of public mass shootings and assault rifles in about 25 percent.³ A 2025 JAMA Network Open study of 184 fatal mass shooting events found handguns present in 78.8 percent, shotguns in 21.2 percent, rifles in 19 percent, and assault weapons in 29.9 percent, categories that overlap because many incidents involve more than one firearm.⁴

Why AR-15-Style Rifles Drive the Deadliest Attacks

Even though handguns are more common, an AR-15-platform rifle has been the weapon in almost every high-casualty school shooting of the past fifteen years.

Sandy Hook Elementary School, Newtown, Connecticut (December 14, 2012). Adam Lanza killed 20 children and six adults with a Bushmaster XM15-E2S, Remington’s version of the AR-15. The rifle was legally owned by his mother, whom he killed before driving to the school.⁵
Marjory Stoneman Douglas High School, Parkland, Florida (February 14, 2018). Nikolas Cruz, 19, used a Smith & Wesson M&P 15.223 rifle he had legally bought at 18 from a federally licensed dealer. He passed an instant background check because he had no criminal record and had never been adjudicated as mentally ill. He killed 17 people and wounded 17 more.⁶⁷
Robb Elementary School, Uvalde, Texas (May 24, 2022). Salvador Ramos, 18, legally purchased two AR-platform rifles from a licensed dealer, a Smith & Wesson M&P 15 on May 17 and a Daniel Defense M4 V7 on May 20, plus 375 rounds of ammunition on May 18. Investigators later recovered 1,657 rounds and 60 magazines. He killed 19 children and two teachers.⁸⁹¹⁰
The Covenant School, Nashville, Tennessee (March 27, 2023). Audrey Hale carried an AR-15 rifle, a 9 mm Kel-Tec SUB2000 pistol caliber carbine, and a 9 mm Smith & Wesson handgun into the school, killing three children and three adults. Hale had legally purchased seven firearms from five local stores between 2020 and 2022.¹¹
Apalachee High School, Winder, Georgia (September 4, 2024). Colt Gray, 14, used a SIG Sauer M400 AR-15-style rifle to kill two students and two teachers and wound nine others. His father, Colin Gray, had bought the rifle as a Christmas present for his then-13-year-old son seven months after law enforcement had questioned the family about online threats of a school shooting.¹²

The reason the death tolls climb when these rifles appear is partly ballistic and partly about capacity. Assault-style rifles fire rounds with up to four times the muzzle velocity of a typical handgun round, causing far more severe tissue damage per bullet.¹³ They are also usually paired with 30-round or larger magazines, letting a shooter fire continuously without reloading. At Parkland, the shooter killed 11 people and wounded 13 in under two minutes.¹⁴

An analysis of 340 mass shootings from 1966 to 2016 found that incidents involving an assault-style rifle averaged 5.2 deaths and 7.6 injuries, compared with 2.9 deaths and 3.2 injuries when no such rifle was present.⁷ A separate analysis of 2015 through 2022 found that mass shootings involving assault weapons averaged 35.4 people shot per incident, versus 6.1 with other firearms.¹³ A study of high-fatality mass shootings from 1990 to 2017 found that attacks involving large-capacity magazines produced a 62 percent higher mean death toll, 11.8 versus 7.3.¹⁵

Where the Guns Come From

The most consistent finding across the research is that underage school shooters get their guns from home. The JAMA Pediatrics study found that 41.8 percent of adolescent school shooters obtained firearms from relatives, 29.6 percent from the illegal market, 22 percent from friends or acquaintances, and just 1.9 percent from licensed dealers. Among those who got guns from relatives, 82 percent did so through theft.¹

A 2019 Secret Service review of 25 school shootings found that 76 percent of student perpetrators took firearms from the homes of parents or close relatives. Nearly half took guns from unsecured or easily accessible locations, and in four cases shooters opened locked safes using combinations or keys they already knew.¹⁶ The Johns Hopkins Center for Gun Violence Solutions has put the figure at roughly 80 percent of school shooters under 18 sourcing firearms from their own homes or those of relatives and friends.¹⁷

Storage practices in gun-owning households make that access easy. More than 50 percent of U.S. gun owners store firearms unlocked, and 55 percent of gun owners with children in the home do not practice safe storage.¹⁷ One study found that in homes where parents believed their children could not access firearms, 22 percent of children reported they could reach one within five minutes.¹⁸

The pattern shifts for older shooters. The Parkland, Uvalde, and Nashville attackers were all 18 or older and legally purchased their weapons from licensed dealers. Federal law allows anyone 18 or older to buy a long gun, including an AR-15-style rifle, from a licensed dealer, while handgun purchases from dealers require the buyer to be 21.¹⁹ For sales by unlicensed private sellers, there is no federal minimum age for long guns at all. People ages 18 to 20 make up just 4 percent of the U.S. population but account for 17 percent of known gun homicide offenders and a disproportionate share of school shootings and public mass shootings.²⁰

After Parkland, Florida raised its minimum purchase age for all firearms from 18 to 21, with exceptions for law enforcement and military.²¹ Seven other states, California, Colorado, Delaware, Hawaii, Illinois, Rhode Island, and Vermont, have also set 21 as the minimum for all firearm purchases.²² At the federal level, the Bipartisan Safer Communities Act of June 2022 did not raise the purchase age but did require enhanced background checks for buyers under 21, including searches of juvenile criminal and mental health records.²³

Ghost Guns and 3D-Printed Firearms

Untraceable firearms assembled from kits or 3D-printed parts, commonly called ghost guns, have appeared in at least four school shootings since late 2021, in Arizona, Maryland, New Mexico, and Kansas.²⁴ No school shooting to date has involved a fully 3D-printed firearm, though students have been caught on school grounds with non-functioning 3D-printed weapons, and police have discovered 3D printing equipment and partially assembled firearms during investigations of teenage suspects. Entry-level 3D printers cost $200 to $300, and there are no federal age restrictions on purchasing the printers or downloading firearm blueprints.²⁵

Who Can Be Held Responsible

Because so many school shooters, especially the youngest ones, use guns owned by relatives, liability has begun to extend beyond the shooter.

Parents Charged With Homicide

In November 2021, 15-year-old Ethan Crumbley killed four students and wounded seven at Oxford High School in Michigan using a gun his parents had bought for him days earlier. His parents had met with school officials about his mental health on the morning of the shooting, after he drew images of a gun and bloodshed on a school assignment, and chose not to take him home.²⁶ In early 2024, James and Jennifer Crumbley were each convicted of involuntary manslaughter and sentenced to more than a decade in prison, the first time parents of a school shooter have been convicted of homicide in the United States.²⁷

Less than a year later, Colin Gray, the father of the Apalachee High School shooter, was charged with second-degree murder, involuntary manslaughter, and cruelty to children for buying the rifle used in the attack and giving it to his son after law enforcement had already warned him about the boy’s online threats. Gray has pleaded not guilty and was on trial as of early 2026.¹²

Safe Storage and Child Access Prevention Laws

Michigan passed a child access prevention law in 2023 partly inspired by the Oxford case, requiring gun owners to store firearms locked and unloaded if a minor lives in or visits the home.²⁶ As of early 2025, 26 states have secure storage or CAP laws of varying strength. Some require firearms to be locked whenever they are not under the owner’s immediate control, including California, Connecticut, Massachusetts, and Oregon. Others impose penalties only after a child actually gains access, including Florida, Texas, and Wisconsin.²⁸ An additional nine states have CAP laws that apply only when an adult recklessly or intentionally provides a firearm to a child. There is solid research evidence these laws reduce youth suicides and unintentional injuries; evidence on whether they specifically reduce school shootings remains inconclusive.¹⁸

Lawsuits Against Manufacturers

Gun makers have long been shielded from most civil suits by the federal Protection of Lawful Commerce in Arms Act (PLCAA). That shield cracked in 2022, when the families of Sandy Hook victims reached a $73 million settlement with Remington Arms, the first time a gun manufacturer was held financially accountable for a mass shooting. The families argued that Remington’s marketing of the Bushmaster XM15-E2S targeted young, at-risk males through militaristic advertising, including an ad with the phrase “Consider Your Man Card Reissued.” The Connecticut Supreme Court had ruled the suit could proceed under state consumer protection law despite PLCAA.⁵

Since 2021, at least eight states have passed firearms industry liability statutes designed to qualify under PLCAA’s “predicate exception,” which permits suits when sellers or manufacturers violate state laws governing firearm sales or marketing.²⁹ In July 2025 the Second Circuit upheld New York’s version of that law.³⁰ In June 2025, the U.S. Supreme Court unanimously dismissed a $10 billion lawsuit brought by Mexico against firearm manufacturers, finding PLCAA barred the claim.

Assault Weapons and Magazine Bans

The federal assault weapons ban enacted in 1994 prohibited the sale of 19 named firearms, including the AR-15, and of magazines holding more than 10 rounds. It expired in 2004 under a built-in sunset provision and has not been renewed.³¹ During the decade the ban was in effect, there were 12 high-fatality mass shootings and 89 deaths; in the 13 years after it expired, there were 48 such events and 527 deaths.¹⁵ As of 2026, 10 states and the District of Columbia ban the sale of assault weapons, and 14 states plus D.C. restrict large-capacity magazines.¹⁴ In 2025, the U.S. Supreme Court declined to hear challenges to Maryland’s assault weapons ban and Rhode Island’s magazine capacity ban.

1
PubMed. Characteristics and Obtainment Methods of Firearms Used in Adolescent School Shootings
2
Healio. Most Guns Used in School Shootings Come From Family Members
3
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4
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5
WHYY. Sandy Hook Families’ $73M Settlement With Remington
6
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7
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16
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17
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18
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19
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20
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21
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22
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23
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24
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25
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26
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28
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29
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31
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