UPPER MARLBORO, Md. — There are a lot of reasons why people love their AR-15 semiautomatic rifles, and it doesn't much matter to them what the haters say.

For some, the gun is a tool, a finely tuned machine that can cut down an animal or intruder, or pierce a distant target, with a single precise shot.

For others, it is a toy, a sleek beast of black plastic and metal that delivers a gratifying blast of adrenaline.

And for many, it is a symbol, the embodiment of core American values — freedom, might, self-reliance.

“There are very few things that serve such a great form and function, and look cool,” said Daniel Chandler, 26, an AR-15 owner here in suburban Maryland. When he takes his AR out of its case at a shooting range, he smiles like he just unwrapped a gift. “There are few things you’ll find that are wonderfully appealing to look at, wonderful exercises in mechanical engineering, and that could save your life.”

This is the side of the AR-15 that many don’t see, or ever consider.

Because an AR-15, or a variant, was used in several mass shootings — including Aurora,Colorado; Newtown, Connecticut; San Bernardino,California; Sutherland Springs, Texas; and Las Vegas, in which a total of 137 people were killed — this civilian sibling of a military assault rifle is an exceptionally polarizing product of modern American industry. The AR-15 and its semiautomatic cousins — they shoot one round for each pull of the trigger - incite repulsion among those who see them as excessive, grotesque and having no place on the civilian market.

It is the focus of multiple attempts at prohibition, which in turn has prompted people to run out and buy more. Such “panic buying” drove sales of AR-15s to record levels during the presidency of Barack Obama and the 2016 presidential campaign. Gun merchants say some buyers are also driven by a fascination with a weapon used in notoriously heinous crimes.

Fears of a ban have subsided under gun-friendly President Donald Trump, and so have sales; gun makers are in the midst of a year-long slump that has driven down prices for AR-style rifles. Those discounts appear to have driven a record number of Black Friday gun background checks.

Devotees say the AR-15 has been wrongly demonized, arguing that the vast majority of owners never use it in a crime, and that despite the rifle’s use in mass shootings, it is responsible for a very small proportion of the country’s gun violence.

Thanks to that ardent following, and shrewd marketing, the AR-15 remains a jewel of the gun industry, the country’s most popular rifle, irreversibly lodged into American culture.

From Vietnam to the mainstream

The AR-15 was developed in the late 1950s as a civilian weapon by Eugene Stoner, a former Marine working for small California startup called ArmaLite (which is where the AR comes from). The gun, revolutionary for its light weight, easy care and adaptability with additional components, entered the mainstream in the mid-1960s, after Colt bought the patent and developed an automatic-fire version for troops in Vietnam, called the M16.

The civilian model wasn’t mass produced until the 1980s, after the original patent expired and a variety of companies began making them. That transformed a specific brand to a more generic offering on which a mini-industry would flourish.

The AR-15 and other semiautomatic rifles also turned up in shootings, fueling a movement to restrict their manufacture and sale. Much of the outrage stemmed from the militaristic appearance of those guns, and their ability to fire rapidly.

But there was also a more visceral reason, involving flesh and blood. AR-15s inflict much more damage to human tissue than the typical handgun, which is used in most shootings. That's largely because of the speed at which projectiles leave the weapons; they are much faster out of the muzzle of an AR-15, or similar rifle, and deliver a more devastating blow to bones and organs. Those projectiles are also more likely to break apart as they pass through the body, inflicting more damage.

“The higher muzzle-velocity projectiles, if they strike an organ, you’re more likely to have severe injury and bleeding and dying than with lower muzzle-velocity munitions,” said Donald Jenkins, a trauma surgeon at the University of Texas in San Antonio and the owner of several guns, including an AR-15.

The backlash peaked in 1994, when President Bill Clinton signed a ban on the sale of many types of semiautomatic rifles deemed “assault weapons,” including versions of the AR-15. Manufacturers continued making versions of the AR-15 that complied with the new law, which was allowed to expire in 2004. That set the stage for an explosion in AR-15 sales.

By then, military-style weapons were becoming a more common sight in America, due largely to the response to the 9/11 attacks. Anti-terror police forces began patrolling cities and transportation hubs, and the wars in Afghanistan and Iraq were covered intimately. That higher visibility seemingly fed a desire among gun owners to get what the troops and cops were using.

With encouragement from the gun industry, the AR-15 grew popular not only among people who enjoyed owning the latest tactical gear, but also among recreational and competitive target shooters, and hunters. Many saw it as a pinnacle of firearms engineering — ergonomic, accurate, reliable.

Graphic: Estimated number of AR-style rifles produced and murder victims by firesarms

“It’s kind of the standard, de-facto rifle now,” said Evan Daire, 23, a gun-range worker in New Jersey who aspires to become a professional target shooter. “No matter what role you’re looking at, it pretty much fills that role.”

Production of AR-style guns has soared since the federal ban expired. In 2004, 107,000 were made. In 2015, the number was 1.2 million, according to the National Shooting Sports Foundation (NSSF), an industry trade association. The organization does not provide sales data, nor does it have 2016 production estimates, but says that year's activity likely broke all records.

Today, one of out of every five firearms purchased in this country is an AR-style rifle, according to a NSSF estimate. Americans nowown an estimated 15 million AR-15s, gun groups say. New AR-15 style guns range widely in price, from about $500 to more than $2,000.

'Destined to be a best-seller'

Chandler is an unlikely AR enthusiast. He grew up outside Baltimore, a city plagued by gun violence, raised by parents opposed to firearms and was friends with kids whose lives had been torn apart by them. For much of his youth he considered himself anti-gun.

Then a well-to-do neighbor was shot in a home invasion. Chandler realized that his family had no weapon to defend itself, and decided to buy a gun when he got old enough.

When he turned 21 and began shopping, Maryland tightened laws in response to the December 2012 mass shooting at Sandy Hook Elementary School in Newtown, Connecticut. That measure banned many types of semiautomatic rifles, so when Chandler eventually decided that he wanted an AR-15, he built one from scratch, adhering to the new restrictions. It’s black and green, with a 16-inch barrel, a collapsible stock and an electronic red-dot sight.

On one of his recent visits to a gun range, Chandler showed what made the AR-15 a cutting-edge gun when it was created, and one reason why it became so widespread. Pushing the gun's "takedown pins" with his fingers, he broke his gun down into its basic components, and within several seconds snapped it back together.

This is why some people compare the AR-15 to a car chassis, others to Legos or Mr. Potato Head. It is relatively easy to take it apart, reassemble it and modify it - including changes to the caliber of ammunition it fires. Those who build ARs from scratch link themselves to a centuries-old American gunsmithing tradition.

“It was destined to be a best-seller because of these qualities,” said Dave Kopel, a gun-rights advocate and research director at the Independence Institute, a libertarian think tank in Denver.

Building an AR-15 at home often begins with buying a "lower receiver," the only part with a serial number and that requires a federal background check. The rest of the core parts are available online. Then there is a seemingly endless array of accessories: barrels, grips, stocks, rails, magazines and scopes.

Chandler loves the AR he built. He admires its simple, efficient mechanics, its precision, and how much fun it brings. He fires almost weekly for target practice, along with a Glock 17 handgun. He’s taken his wife to the range with him, and she’s become an AR fan herself, preparing to build her own.

Chandler, who is black, doesn't have many friends who enjoy guns as much as he does. So he has created a firearm-focused Instagram page to find similarly minded people, many of them millennial first-generation gun owners like himself.

“The AR-15 makes sense, and I think that’s why more people my age are gravitating to it,” Chandler said.

The hashtag #ar15 has over 1.7 million tags on Instagram, with users uploading by the minute.