On a recent Monday, the Smith & Wesson 9mm Model SD9VE handgun was selling briskly at the Westside Armory, 1,900 square feet of guns and ammo in a tidy shopping mall anchored by a Vons grocery and also featuring a nail salon, Starbucks, and Buffalo Wild Wings. The mall is 15 minutes southwest of the Las Vegas Strip but feels worlds away from the garish casinos. The store's owner, Cameron Hopkins, bundles the SD9VE with a Streamlight TLR-3 flashlight, which attaches beneath the barrel, as well as two 16-round magazines. The package goes for $399.99, down from $526.70.

"It's a nightstand pistol," Hopkins says to one potential customer, a tall man in a blue sweatsuit. "Perfect for home defense, and you can't beat the price." The guy ponders for 20 minutes, musing about the danger of nighttime intruders entering his house from an adjacent golf course, and then buys one.

Handguns at Westside Armory—Glock, Smith & Wesson, Colt, and Sig Sauer—are displayed in waist-high glass cases. Rifles and shotguns hang from the walls. To get to the firearms, customers first pass racks of holsters, goggles, ear protection, magazines, speed loaders, range bags, cleaning solutions, and paper targets—zombies, grimacing thugs, Osama bin Laden. Boxes of ammunition line one wall, interspersed with such novelties as red-white-and-blue colored ceramic lawn gnomes bearing miniature guns and hand grenades.

The main business of Westside Armory, though, is handguns, mostly semiautomatic pistols, which carry ammunition in rectangular magazines that snap into the grip. Handgun sales outnumber rifle and shotgun sales by about 20 to 1, although some of the most expensive items the store sells are custom-made rifles that retail for $2,500 or more.

Westside Armory took in $190,000 in December, its highest mark since opening in the summer of 2014. That's consistent with a nationwide boom. In December, the Federal Bureau of Investigation did a record 3.3 million background checks, half a million more than the previous monthly high in the wake of the Newtown, Conn., elementary school massacre in 2012.

"It's been this way for the last seven years," since President Obama got into office, says Mike Moore, Westside's account manager at RSR Group, a large national gun-and-ammunition wholesaler based in Winter Park, Fla. Moore and others in the industry marvel at the staying power of what they call "the Obama surge"—elevated sales driven by the (unfulfilled) fear of tougher federal gun control.