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A line of ambulances leaves a King Soopers grocery store where 10 people died  in a shooting in Boulder, Colo. (AP Photo/David Zalubowski) A line of ambulances leaves a King Soopers grocery store where 10 people died  in a shooting in Boulder, Colo. (AP Photo/David Zalubowski)

A line of ambulances leaves a King Soopers grocery store where 10 people died in a shooting in Boulder, Colo. (AP Photo/David Zalubowski)

Jon Greenberg
By Jon Greenberg March 24, 2021

AR-15 style weapons were used in 10 major shootings

If Your Time is short

  • AR-15 is a shorthand term for a category of semi-automatic rifles that share certain characteristics.

  • A Twitter post correctly describes 10 out of 11 mass shootings in the past decade as involving AR-15 style weapons.

  • One shooting on the list involved a semi-automatic rifle that has different internal mechanics than the AR-15 style weapon.

Semi-automatic rifles in the AR-15 style have been the weapon of choice in numerous deadly mass shootings. Until 2004, they were banned as assault weapons under federal law. Gun control advocates have focused on firearms of this sort for decades.

In the arrest warrant for the gunman in the March 22 shooting that killed 10 people in a Boulder, Colo., supermarket, police describe one of the weapons as "a rifle (possible AR-15)."

Adam Best, an entrepreneur and progressive activist with over 189,000 followers on Twitter, posted a list with 11 other shootings over the past decade that he said involved an AR-15.

AR-15 once referred to a specific model of rifle, but the label has come to be recognized in recent decades as a shorthand term for a category of firearms that share certain characteristics. (The AR stands for ArmaLite, the original maker of the AR-15 rifle.) They are semi-automatic, which means the trigger must be pulled to fire each round, and a new round moves into the chamber after each pull. As rifles, they have a general shape and configuration, and can be customized with a choice of grips, triggers, stock, and more.

We reviewed news and law enforcement reports on the shootings listed in Best’s tweet.  We verified that all but one did involve at least one weapon in the AR-15 style. The possible exception was the deadly attack on the Pulse nightclub in Orlando, Fla.


June 12, 2016: A gunman began shooting inside the Pulse, killing 49 people and wounding 53. Orlando Police officers shot and killed him after a three-hour standoff. One of the weapons was a SIG Sauer MCX. The SIG Sauer takes a lot of the form and functions of the AR-15 but with reworked internal mechanics and some other changes. For example, the SIG Sauer is built to handle a different caliber round than the standard AR-15.

The two weapons have so much in common that the Bureau of Alcohol, Tobacco and Firearms called the SIG Sauer used in Orlando a ".223 caliber AR type rifle." 


Feb. 14, 2018: A gunman opened fire with a semi-automatic rifle at Marjory Stoneman Douglas High School in Parkland, Fla. He killed 17 people and injured 17 others. 

Las Vegas

Oct. 1, 2017:  A gunman opened fire on concertgoers at the Route 91 Harvest music festival on the Las Vegas Strip. From his 32nd-floor hotel room, he killed 60 people and wounded 41. Police found 14 AR-15s, plus other weapons in the gunman’s hotel room.

Aurora, Colo.

Featured Fact-check

July 20, 2012:  A gunman fired into the audience at a movie theater. He killed 12 people and injured 58 others.

Sandy Hook

Dec. 14, 2012: A gunman shot and killed 26 people, including 20 children between 6 and 7 years old, and six adult staff members at the Sandy Hook Elementary School in Newtown, Conn.

Waffle House

April 22, 2018: A gunman opened fire inside a Waffle House restaurant in Nashville, Tenn. He killed four people and injured two others. 

San Bernardino

Dec. 2, 2015: A married couple opened fire at a San Bernardino County (Calif.) Department of Public Health training event and Christmas party. They killed 14 people and injured 22 others. 


Aug. 31, 2019: After shooting a police officer and another person, a gunman killed a postal worker, commandeered his van and fired on others on a Texas highway. He killed seven people and injured 25 others. 

Poway synagogue

April 27, 2019: A gunman fired shots inside the Chabad of Poway synagogue north of San Diego. He killed one woman and injured three others.

Sutherland Springs

Nov. 5, 2017: A gunman opened fire during services at the First Baptist Church in Sutherland Springs, Texas. He killed 26 people and wounded 20 others.

Tree of Life Synagogue 

Oct. 27, 2018: A gunman opened fire during services at the Tree of Life – Or L'Simcha Congregation in Pittsburgh. He killed 11 people and wounded six.

Our ruling

A tweet said an AR-15 style weapon was used in the Boulder mass shooting and 11 past mass shootings. At least one AR-15 style weapon was used in 10 of the examples. 

For the 11th — at the Pulse nightclub — the weapon used had some internal differences from the AR-15 style, but the ATF characterized it as an AR-15.

With that technical difference, we rate this claim Mostly True.


Our Sources

Adam Best, tweet, March 22, 2021

County of Boulder, warrant for arrest, March 23, 2021

National Shooting Sports Foundation, Understanding America’s Rifle, accessed March 23, 2021

Tactical Life, Sig Sauer’s MCX Rifle: An Elite Modular Weapons System, June 30, 2015

U.S. Bureau of Alcohol, Tobacco and Firearms, tweet, June 12, 2016

NBC News, AR-15 Style Rifle Used in Orlando Massacre Has Bloody Pedigree, June 15, 2016

Time, The Florida School Shooter Used An AR-15 Rifle. Here's What to Know About the Gun, Jan. 15, 2019

KTNV News, Guns and evidence from Las Vegas shooter Stephen Paddock, Jan. 20, 2018

Washington Post, The Las Vegas shooter modified a dozen rifles to shoot like automatic weapons, Oct. 3, 2017

New York Times, Aurora Gunman’s Arsenal: Shotgun, Semiautomatic Rifle and, at the End, a Pistol, July 23, 2012

NBC News, Supreme Court allows Sandy Hook families' lawsuit against gunmaker to go forward, Nov. 12, 2019

Tennessean, Waffle House shooting: Police confirm AR-15 used in attack at Antioch diner, April 23, 2018

Wall Street Journal, Man Who Provided Weapons in 2015 San Bernardino Mass Shooting Sentenced to 20 Years, Oct. 23, 2020

U.S Justice Department, Man Who Sold Midland/Odessa Shooter AR-15 Used in Massacre Sentenced for Unlicensed Firearms Dealing, Jan. 7, 2021

New York Times, What to Know About the Poway Synagogue Shooting, April 29, 2019

Atlanta Journal Constitution, "He had an AR-15, but so did I." Sutherland Springs hero hailed by NRA, May 6, 2018

U.S. Justice Department, Additional Charges Filed in Tree of Life Synagogue Shooting, Jan. 29, 2019

PolitiFact, The facts on mass shootings in the United States, Nov. 8, 2017

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AR-15 style weapons were used in 10 major shootings

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