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At the GunRunners Gun Show outside Atlanta, the line stretches out the door and around the corner. Dozens of people are waiting, ready to fork over big bucks for everything from pistols to high capacity magazines.

Here, the hottest seller isn't a shotgun, handgun, or even a pair of Angie Whitaker's .22-caliber bullet casing earrings. It's the AR-15 semiautomatic rifle.

"We probably brought maybe 100 AR-15s with us," said vendor George Mazzant, from On the Square Gun & Pawn. "I'd like to sell half of them, and, I'm sure we will. We've been doing that well every weekend."

Mazzant is running a special, selling Stag Arms AR-15 rifles for $999. It's an offer that's too good for show attendee Ken Farrell to pass up.

"I always wanted one," said Farrell. "I'm getting it now just in case I can't later. Since the rumors of the bans, the prices have skyrocketed."

"When you tell the American public that they're not going to have something, they want it," said Mazzant.

The AR-15 is at the heart of the gun control debate. The civilian version of the M16, it's the most popular rifle in the country, with some 4 million in the hands of gun owners and a wildly passionate fan base. Its use in the mass shootings in Newtown, Conn., and Aurora, Colo., thrust the AR-15 into the national spotlight.

"The AR-15 is, essentially, a gun that was designed to inflict maximum casualties, death, and injury, in close to medium range. That's what it does," said gun control advocate and former NRA member Tom Diaz. "The real problem is that we allow that kind of firepower to come into a theater or into a first-grade class."

"It's a question of cosmetics. It's not a question of functioning," said Steve Sanetti, president of the National Sports Shooting Foundation. "The rifles are sane, safe, reliable types of firearms used by millions of citizens for lawful purposes. They are not just killing machines."

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But if the gun control debate has some people up in arms, it's had others buying them up — an unintended side effect of the push for stricter gun laws. The most recent measures — President Barack Obama's attempt to strengthen gun laws by expanding background checks, limiting large ammunition magazines and banning certain military-style firearms — were defeated on the Senate floor earlier this month.

Just the threat of a ban has been a boon to the gun business.

"[It's] been a very, very busy year for us," said Mark Malkowski, president of Stag Arms in New Britain, Conn. "Right now we're at about a year's back order, 70,000 rifles at this point."

Connecticut recently passed some of the toughest gun laws in the country, banning the sales of AR-15s. Malkowski has since announced he might be forced to move his company out of the state — taking some 200 jobs with it. Stag Arms is one of more than 30 companies that make the AR-15; together they sell some 800,000 rifles a year, nearly all for the U.S. market.

"The AR-15 now is probably the Number 1 economic engine in the gun industry," said Larry Hyatt, owner of Hyatt Gun Shop in Charlotte, N.C. "We sell every one we get, almost as quick as they come in. We've never seen the demand that's here today."

Gun store owners and analysts alike say it's one of the bestselling guns in the country; roughly $1 billion of the estimated $4 billion firearms industry is made up of sales of AR-15 rifles and their accessories.

"These are expensive guns that people think about a lot before they buy them," said Hyatt. "They're not protesting on the street against the government, they're buying AR-15s and ammunition. It's not advertising, it's not marketing, it's political."

Politics coupled with shifting consumer preference are big drivers of the market, said Wedbush Securities analyst Rommel Dionisio.

"In the last two years, the market has exploded," he said. "It's a fad; it's the cool, new rifle. People used to hunt with bolt action rifles. Now they're using the modern sporting rifle."

According to the sports shooting foundation, an average AR-15 runs about $1,000. They also say the average owner has more than one rifle and spends an additional $483 for accessories. It's a pricey purchase that Diaz says is benefiting from years of industry marketing.

"The names you see now are 'modern sporting rifle,' 'tactical rifle,' " he said. "Those are all just euphemisms for 'assault weapon.' They're being very rational as marketers and as businesses — and as industries. They're only doing what cellphone companies do to make cellphones look different and be more attractive. The difference is what they're selling is lethality."

"They're selling today's rifle," said the foundation's Sanetti. "We call it the modern sporting rifle. And that's exactly what it is."

Whether it's called a modern sporting rifle or an assault rifle, for Atlanta gun show vendor Mazzant, AR-15s are just good business.

"Today was one of the better sales days with ARs," he said. "Everybody in the whole place was lining up to buy them."

Mazzant started off with 100 AR-15 rifles. By the end of the day, he didn't have a single one left.

Tune in to America's Gun: The Rise of the AR-15 on CNBC Prime, Thursday April 25th at 10p ET/PT.