Alex Schachter, a 14-year-old marching band member who was killed in the Parkland, Florida, school shooting, would have graduated this year from Marjory Stoneman Douglas High School.

When the accused Parkland shooter stormed into Stoneman Douglas High School in February 2018, he was armed with an AR-15-style rifle, killing Alex and 16 others.

According to the National Shooting Sports Foundation, a national trade association for the firearm industry, over 20 million AR-15-style rifles are legally in circulation in the United States. Although this represents a small proportion of the country’s roughly 400 million guns, the popularity of AR-15-style rifles has grown “exponentially” since the federal assault weapons ban expired in 2004, according to Mark Oliva, the NSSF’s public affairs director.

Because AR-15-style rifles are so versatile, with the ability to add scopes and change both the length and size of the barrel, they have become a popular weapon among many Americans, particularly hunters.

However, as these weapons become more popular, their use in mass shootings is increasing, according to Louis Klarevas, a research professor at Teachers College, Columbia University who specializes in gun violence and safety. “Most of the deadly high-profile mass shootings in the last decade were perpetrated with assault weapons, particularly AR-15-style assault rifles,” Klarevas said, citing Sandy Hook, San Bernardino, Orlando, and Las Vegas.

This class of firearm, also known as “assault weapons” or “military-style rifles,” can include a wide range of weapons, not just the more well-known rifles like the AK and AR-15 series. According to the California Attorney General’s Assault Weapons Identification Guide, the term “assault weapon” generally encompasses a wide range of models, including the UZI rifle and pistol, the Beretta AR-70, the SKS rifle, and others. AR-15 style rifles, such as the Smith & Wesson M&P15 and the Ruger AR-556, are “modeled on the AR-15 platform and fire the same caliber cartridges,” according to Klarevas. 

Along with their use in hunting, AR-15-type weapons connote patriotism for some Americans, which can be traced back to the M16 military rifle, which became popular during the Vietnam War, according to Garrett.

However, an AK-47 was used to kill five children at a Stockton, California, elementary school in 1989, prompting California to become the first state to enact an assault weapons ban, according to Klarevas. In 1993, there were two other high-profile semiautomatic pistol mass shootings, one in San Francisco and one on a Long Island Rail Road commuter train.

These shootings sparked President Bill Clinton’s signing of the Federal Assault Weapons Ban in 1994, which prohibited the manufacture, sale, transfer, and possession of these types of firearms.

Klarevas wrote in a report he issued last year as an expert witness in a federal court case challenging California’s assault-weapons ban that the federal law resulted in a decrease in gun massacre incidents involving six or more victims. According to his report, when compared to data from 1984 to 1994, the United States saw a 43 percent drop in gun massacre deaths and a 26 percent drop in gun massacre deaths involving assault weapons from 1994 to 2004.

Congress did not renew the federal ban, which expired in 2004. Gun massacre incidents involving these weapons then increased 167 percent from 2004 to 2014, according to Klarevas’ report, and active shooter incidents with different guns overall have been steadily increasing over the last two decades, according to FBI data, which does not break down murders by exact model of gun used.

While there is no federal assault weapons ban in place at the moment, Washington, D.C., and seven states – California, New Jersey, Hawaii, Connecticut, Maryland, Massachusetts, and New York – have banned the possession of certain types of these firearms, with the rules varying by state. “In the past 30 years, accounting for population, states with assault weapons bans experienced 54 percent fewer gun massacres involving the use of assault weapons and 67 percent fewer deaths resulting from such attacks perpetrated with assault weapons,” according to Klarevas’ report.

In many rural and suburban areas, fully and semi-automatic rifles hold a practical value, such as for defending property, and a familial value, to pass down weapons to future generations.