Days after his 18th birthday a man bought two AR-15 rifles and used one to kill 21 people, including 19 children, at a Uvalde, Texas elementary school in May 2022.
Two weeks before that, an 18-year-old man used a modified AR-15 to kill 10 people and injure three more in a Buffalo, New York grocery store.
The same type of gun has also been used in at least 11 other mass shootings since 2012, according to USA Today. It's also used by thousands of Americans every day for hunting and target shooting.
What is an AR-15 rifle, and why is it so popular?
What is an AR-15 rifle?
An AR-15 is a semi-automatic or self-loading rifle that has been called "America's rifle" by the NRA with well over 15 million sold by 2019. "Semi-automatic," as opposed to "automatic," means that the weapon's operator must pull the trigger to fire each shot. The rifle then automatically reloads. An automatic weapon continues to fire as long as you hold down the trigger, and is (mostly) banned in the U.S.
"AR-15s are the most commonly used rifles in marksmanship competitions, training, and home defense," according to the NRA.
An AR-15 is not a specific model, but a style. It's the civilian variation of the ArmaLite AR-15, a variant of the AR-10 designed by Eugene Stoner in the 1950s, that was extremely lightweight, easy to care for and highly adaptable. ArmaLite sold the patent to Colt in the 1960s and they developed an automatic-fire version for the military called the M16. After Colt's patent ran out, other manufacturers began making their own versions.
What does AR-15 stand for?
AR stands for ArmaLite Rifle, named after the company that developed it. AR does not stand for "assault rifle" or "automatic rifle."
Is an AR-15 an assault rifle? What is an assault weapon?
That is a very contentious question.
According to the federal government as described in the Violent Crime Control and Law Enforcement Act of 1994 (known as the Assault Weapons Ban), the definition of assault weapon included some specific semi-automatic models by name and listed other firearms that included some specific features. For semi-automatic rifles, that meant being able to accept detachable magazines and two or more of the following: a folding or telescopic stock, pistol grip, bayonet mount, a flash suppressor and/or a grenade launcher.
More generally since then, the federal government has usually used the term to refer to a military-style weapon, either semi-automatic or fully automatic, capable of firing multiple rounds.
But pro-gun advocates and the gun industry say that "assault rifle" should only apply to military weapons that are either fully automatic or have the capability of switching between semi-automatic and fully automatic, and that the features listed in the federal Assault Weapons Ban were simply cosmetic.
According to the NSSF, the Firearm Industry Trade Association, "AR-15-style rifles can look like military rifles, such as the M-16, but by law they function like other semiautomatic civilian sporting firearms, as they fire only one round with each pull of the trigger." Instead, they refer to the AR-15 as a "modern sporting rifle" or MSR.
Is an AR-15 a machine gun? What is a bump stock?
The AR-15 rifle is not a machine gun (which is not quite the same thing as an automatic rifle), but it can be modified to function like an automatic rifle when a "bump stock" is used.
In October 2017, a Las Vegas gunman used 23 different weapons to murder 58 people. Of the 23 guns, several AR-15 rifles were found in his hotel room with a bump stock attached. Following this shooting, President Donald Trump banned bump stocks.
New FBI active shooter data: Incidents up 52% in 2021, more lethal than 2020 by 171%
Why is the AR-15 so popular?
It's lightweight. It's rugged. It's accurate and has relatively little recoil. It's easy to modify, with plenty of accessories to make it more accurate, more comfortable, and more personal. Some gun owners enjoy a weapon that can be made to look like military hardware.
The NRA said "the AR-15 has soared in popularity" because it's "customizable, adaptable, reliable and accurate." It is also versatile and can be used for "sport shooting, hunting and self-defense situations," the NRA said, adding the ability to "personalize" so many of the rifle's components "is one of the things that makes it so unique."
"Like the Swiss Army knife, the popular AR-15 rifle is a perfect combination of home defense weapon and homeland defense equipment," said U.S. District Judge Roger Benitez when he overturned California's assault weapons ban in 2021. "Good for both home and battle."
But a big reason for the AR-15's popularity is its cost.
How much does an AR-15 cost?
New AR-15 rifles can sell for $400 to $2,000 and nearly every major gun manufacturer produces one. Ammunition is inexpensive and can be bought in bulk online, and magazines are interchangeable between manufacturers.
Why is the AR-15 so dangerous?
The AR-15 was designed to inflict what one of its designers called "maximum wound effect." AR-15s have a higher muzzle velocity than some other rifles and bullets leaving them at such a fast speed — nearly three times the speed of sound — cause more damage to bones and organs. AR-15 ammunition is also more likely to break apart inside a body, causing even more damage.
K-12 School Shooting Database: What a Florida man's school shooting database can tell us about gun violence on campuses
How many rounds can an AR-15 fire in a minute?
Without modifications such as a bump stock, an AR-15 can fire about 60 rounds a minute. A 30-round magazine is fairly standard with MSRs but ammunition magazines ("drums") holding up to 100 rounds can be changed in just a few seconds. Some states currently cap the capacity to 10 or 15 rounds.
Large magazines, or those containing more than 10 rounds, played a role in at least 86 mass shootings since 1980, according to a report from the Violence Policy Center, a national nonprofit that advocates for gun control.
Was an AR-15 used in the Pulse nightclub mass shooting?
Close, but not quite. A 29-year-old man used a Sig Sauer MCX and a 9mm Glock semi-automatic pistol to kill 49 people and injure 50 at an Orlando nightclub before he was killed.
The Sig Sauer MCX is marketed as an MSR and is very similar to the AR-15. However, as explained in a Slate analysis, it is not considered an AR-15 because it uses a gas piston system to propel bullets from within the gun instead of a direct impingement system.
Covering mass shootings: Why you won't see pictures of mass shooting suspects on our front page
Was an AR-15 used in the Parkland, Florida high school mass shooting?
Yes. Police say a 19-year-old man used a Smith and Wesson M&P15, that manufacturer's version of the AR-15, to kill 17 people at Marjory Stoneman Douglas High School in Parkland, Fla.
Cruz trial testimony delayed: Nikolas Cruz death sentencing trial delayed again; testimony now slated to start June 27
Worst school shootings in U.S. history: Parkland, Columbine, Sandy Hook. Texas' Robb Elementary adds to list of worst school shootings in U.S. history
How many mass shootings have involved an AR-15?
Here is a list of mass shootings in the U.S. that featured AR-15-style rifles by themselves or in addition to other weapons during the last 35 years, courtesy of the Stanford Geospatial Center and Stanford Libraries and USA TODAY research:
June 1, 2022: Tulsa, Oklahoma (Dr. Preston Phillips medical center, 4 killed)
May 24, 2022: Uvalde, Texas (Robb Elementary School, 21 killed, several wounded)
May 17, 2022: Buffalo, New York (Tops Friendly Market, 10 killed, 3 wounded)
March 10, 2021: Boulder, Colorado (King Soopers grocery store, 10 people killed, 3 wounded
Aug. 31, 2019: Midland/Odessa (West Texas cities, 7 killed, 25 wounded)
Apr. 27, 2019: Poway synagogue (near San Diego, 1 killed, 3 wounded)
Oct. 27, 2018: Tree of Life Synagogue (Pittsburgh, 11 killed, 6 wounded)
April 22, 2018: Waffle House (Nashville, Tennessee, 4 killed, 3 injured)
Feb. 14, 2018: Parkland, Florida (Marjory Stoneman Douglas High School, 17 killed, 17 wounded)
Nov. 5, 2017: Sutherland Springs (rural Texas church service, 26 people killed)
Oct. 1, 2017: Las Vegas (music festival, 58 killed, hundreds wounded)
June 12, 2016: Orlando, Florida (Pulse nightclub [not an AR-15 but very similar], 49 killed, 50 wounded)
Dec. 2, 2015: San Bernadino, California (holiday office party at Inland Regional Center, 14 killed, 21 wounded)
Dec. 14, 2012: Sandy Hook Elementary School (Newtown, Connecticut, 27 people killed)
June 20, 2012: Aurora, Colorado (Century 16 movie theater, 12 killed, 58 wounded)
Oct. 7, 2007: Crandon, Wisconsin (apartment, 6 killed, 1 wounded)
Feb. 24, 1984: Los Angeles (49th Street Elementary School, 2 killed, 12 wounded)
America's favorite rifle: Why the AR-15 keeps appearing at America's deadliest mass shootings
Are AR-15s legal in Florida? What are Florida's gun laws?
After the 2018 Marjory Stoneman Douglas High School massacre Florida increased the minimum age for buying rifles, shotguns and other long guns to 21.
Research shows that “18-to-20-year-olds’ brains are still developing, that they are at higher risk of using firearms to commit crime and attempt suicide, and that they are disproportionately likely to be victims of firearm-related violence,” according to the brief filed by groups seeking stricter gun control measures.
The NRA has challenged this law, saying it is unconstitutional “because it is inconsistent with the text, history, and tradition of the Second Amendment.”
AR-15s are legal for adults 21 and older in Florida who are legally permitted to own firearms. No state permit is required.
Changing Florida's gun laws: What does 'constitutional carry' mean and how would it change gun laws in Florida?
Contributing: William Cummings, Bart Jansen, USA Today
C. A. Bridges is a Digital Producer for the USA TODAY Network, working with multiple newsrooms across Florida. Local journalists work hard to keep you informed about the things you care about, and you can support them by subscribing to your local news organization. Read more articles by Chris here and follow him on Twitter at @cabridges
This article originally appeared on Fort Myers News-Press: AR-15: What it is, what it can do, and why so many mass shooters like them