NUMBER OF AR-15S IN U.S. IS UNKNOWN

20-round magazine, was easy to disassemble and was marketed, in one of Colt’s early advertisements, to hunters, campers and collectors.

Billed as “America’s rifle” by the National Rifle Association, the AR-15 is less a specific weapon than a family of them. When Stoner’s rights to the gas system expired in 1977, it opened the way for dozens of weapons manufacturers to produce their own models, using the same technology. The term AR-15 has become a catchall that includes a variety of weapons that look and operate similarly, including the Remington Bushmaster, the Smith & Wesson M&P15 and the Springfield Armory Saint.

Over the ensuing decades, as the U.S. military modified the M16’s exterior to allow for accessories such as sights, grips and flashlights, the civilian market followed. Today, gun enthusiasts consider the AR-15 the Erector Set of firearms. Online message boards, video games and advertisements all provide how-to guides for customizing the rifle.

But the guns were taken off shelves after President Bill Clinton signed a law in September 1994 banning what Congress called “assault weapons.” Prompted by a string of mass shootings — including one in 1989 in Stockton, Calif., in which five children were killed and 32 wounded in a schoolyard — the legislation stopped production of civilian rifles like the AR-15, and introduced the term “assault weapons” to the public.

The number of assault weapons recovered by police in crimes and reported to the Bureau of Alcohol, Tobacco, Firearms and Explosives dropped sharply after the ban was carried out, according to a Justice Department report.

But it stops short of directly tying the ban to a decrease in gun violence, and the ban’s broader effect remains in dispute. Gun rights advocates say loopholes allowed for the sale of slightly modified versions throughout the ban. Its defenders cite law enforcement statistics showing a drop in the criminal use of automatic and semiautomatic weapons during that time.

The number of rifles manufactured in the United States has steadily increased since the ban ended through congressional inaction when the ban sunset in 2004, though it is not clear how many are semiautomatic firearms. Some 3.7 million rifles were manufactured in the United States in 2015, the most recent year for which the ATF has publicly available data.

Determining the true effect of the ban is all but impossible because federal regulations prohibit the government from tracking the guns. Though gun industry lobbyists touted the popularity of AR-15S, no public information is available on how many Americans own them, where they are bought or concentrated, or exactly how many exist.

Explosion in popularity

Culturally, the ban did what marketers could not: In outlawing it, the government made the AR-15 tantalizing.

“If you want to sell something to an American, just tell him that he can’t have it,” said Mark Westrom, who owned Armalite, the gun’s original manufacturer.

When the ban ended, enthusiasts could finally buy what for a decade had been forbidden.

And when the AR-15 reappeared in gun stores that fall, American culture had changed. Now, this civilian-model military rifle was being sold amid not only a swell of anticipation but also post-9/11 patriotism and at the height of the wars in Iraq and Afghanistan.

Special Operations forces were being mythologized in news segments, shown carrying their rifles through the desert in imposing tactical gear. Children were shooting the AR-15’S military equivalent in wartime video games. Manufacturers designed rival versions, creating a competitive market that made the AR-15 more affordable.

“So you want to buy a rifle like our troops are using in Iraq?” National Public Radio asked in November 2004. “Well, step up to the counter and tell the man what you want.”

Gun store owners scrambled to meet demand, contemporaneous news accounts show. Shops that historically sold traditional bolt-action guns and older firearms started stocking AR-15S.

Steve Clark, whose family has owned Clark Brothers Gun Shop in Warrenton, Va., since 1956, said his customers were drawn to newer and more modern rifles.

“If the whole world went to ARS, that’s what I’d be selling,” said Clark, who prefers older firearms for what he views as superior craftsmanship. “It would make me sad, but I’m going to sell them what they want.”

AR-15 owners, asked why they bought the firearms, cited recreation as well as the larger mythology that has enveloped the rifle of embodying freedom and the Second Amendment.

Joshua Boston, a Marine who spent two deployments in Iraq and two in Afghanistan and owns several AR-15S, said he kept them for personal defense. He is looking for the serial number of his old military rifle so he can engrave both it and the Colt logo onto the AR-15 he plans to give years from now to his son, now 11 months old.

Chris Cerino, a former federal law enforcement officer and firearms instructor in Ohio, said he hated the AR-15, until he used one. “It was so fun to shoot,” said Cerino, 48. Now, he and his wife, who has a purple AR-15, love them.

“It’s an icon,” he said. “It’s a symbol of freedom. To me, it is America’s rifle.”

Critics say the firearm’s branding positioned it for notoriety. Josh Koskoff — a lawyer who represents parents of victims of the 2012 shooting at Sandy Hook Elementary School in Newtown, Conn., in a lawsuit against the gun manufacturer Remington — cited a concerted effort by the gun industry after the assault weapons ban to use the AR-15 to shape popular opinion around semiautomatic weapons — rebranding them as “modern sporting rifles.”

“When they market it to young men, there’s no ‘sporting rifle’ angle to it,” Koskoff said. “It’s all military. It’s all violent. And it’s all incendiary marketing.”

Indeed, the AR-15 is also inextricably linked to tragedy. Mass shootings are central to the gun’s narrative, and its popularity. Police departments stocked up on them after a string of massacres in the 1990s. Some supporters attribute their fondness to fear of being outgunned should they encounter an aggressor. Hobbyists, like Swarey, 23, have swarmed to gun shops after mass shootings, fearful that they could be a catalyst for the government to outlaw them again.

“It was right around the time of the first school shooting that made the news and scared everybody,” Swarey said of buying his first AR-15 about five years ago, when, he said, the Sandy Hook elementary school shooting was fueling talk of another assault weapons ban. “It was one of those things, that I wanted to get one before they were impossible to get.”

‘Chickens coming home to roost’

Compared with pistols, assault rifles are used rarely in shootings. According to FBI statistics, 374 people were murdered with any kind of rifle in 2016; 7,105 were killed by a handgun.

But the AR-15 has been a recurring character in some of the United States’ most infamous violent crimes. Adam Lanza used his to kill 20 children and six educators at Sandy Hook. Stephen Paddock used an enhanced Ar-style gun to kill 58 concertgoers and wound hundreds on the Las Vegas Strip in October. A month later, Devin Kelley murdered 26 congregants with a Ruger AR-15 variant at a church in Sutherland Springs, Texas. And the rampage last month at Marjory Stoneman Douglas High School in Parkland, Fla., renewed calls for assault-style rifles to be banned — a common refrain after mass shootings.

It is unclear when and how the rifle worked its way into the United States’ lexicon of violent crimes. In 1982, George E. Banks shot to death 13 people with the weapon, and in 1997, an AR-15, among other semiautomatic military-style rifles, was used in the North Hollywood shootout, a daytime robbery in California that devolved into a nearly hourlong firefight and was televised live across the country. During the gunbattle, police officers were forced to run to a local gun store and take rifles to try to contend with the robbers’ firepower and body armor. Afterward, police departments across the country started making AR-15S standard issue for officers.

Koskoff, the lawyer for Sandy Hook victims, criticized the marketing of the AR-15 as hypermasculine and inflammatory, aimed at attracting young men, “ringing the bell of the lone gunman.”

“What we’re seeing right now with the increasing velocity of shootings with AR-15S is a little bit of a ‘chickens coming home to roost’ scenario,” he said. “They sold so many to so many, and so indiscriminately to this younger demographic, that it’s just become a risk that increases with each sale.”