Kalashnikovs, the Soviet-designed rifles that became the basic killing tool of armies and militants around the globe, are making a new conquest: the United States.

At his workshop in Manchester, New Hampshire, Owen Martin expertly dismantles the Kalashnikov brought to him by a friend. "I'm doing pretty good," the satisfied young gunsmith says.

Also in the workshop is Martin's friend Mat Devito, a private trainer for would-be marksmen. Devito says the Kalashnikov is all the rage -- he's just finished introducing the military style weapon to 40 women, aged between 15 and 54, who'd "never touched a gun before."

He says he's seen a "huge rise" in applications for shooting lessons at his Down Range Firearms Training school, with the Kalashnikov course getting particular demand.

Martin, 30, opened his gunsmith shop, called Snake Hound Machine, nine months ago to meet demand from Kalashnikov owners, some of whom want the powerful rifle for defense at home and others for hunting.

His specialty is in customizing Kalashnikovs, which are manufactured at Russia's Izhmash factory, made at licensed factories in the United States or imported from eastern European states like Romania.

"I started my company legally in March and I have grown exponentially since then," he said. "I am turning a profit at this point."

The rifles he handles are based on AKMs, the generation of Kalashnikov that followed the original, famous AK-47. Demand by customers for tweaking everything from the stocks to the triggers and sights, is high.

There are an estimated 310 million firearms in private hands in the United States -- as many as there are inhabitants.

According to The New York Times, sales by Izhmash to the United States of Kalashnikov civilian rifles and shotguns -- sold under the brand name Saiga -- went up 50 percent last year.

At Izhmash, about 40 percent of the civilian arms, which cannot be fired in full automatic mode, are exported to the United States, where they can sell for as little as just under $500.

The success of the Kalashnikov -- made by America's former Cold War enemy and standard issue for Taliban guerrillas and others battling the United States around the world -- is the same as everywhere else.

"It's a good reliable rifle (and) extremely cheap," Martin said. "The reason why I am such a huge fan is (that) they are the most reliable semi-automatic rifles ever made. Plus the ammunition is extremely inexpensive."

According to Martin, licensed gun dealers are even running short on stock "because sales are so high."

Asked why a gun designed for war would be so popular, Martin said "a lot of people get AKs specifically for the use of home defense, and protecting their lives and liberties and properties."

"People are worried by invasion here, people worry about people taking our gun rights away," Devito added, mentioning fears among firearms fans that President Barack Obama might restrict gun ownership rights if reelected -- something Obama has never proposed.

There's also something of a mini arms race where to be sure of self-defense, something heavier is required. "Back in the days, people had just pistols. Now they are getting more into rifles, especially the AK-47," Devito said.

Devito had come in to see Martin ahead of a wild boar hunting trip in Louisiana and he wanted to have several of his Kalashnikovs tested.

Another customer, Mat Livingston, a part-time construction worker, had just bought his first Kalashnikov and wanted it modified to "make it easier to operate, to make it tougher."

Livingston said he already had 10 firearms, but "I didn't have any type of rifle that I can use to defend myself and the people I love."

Pending any emergency, he plans to use the gun to shoot deer. He practices at least twice a week at the property of his mother, Christine Holmes.

Holmes, a gun enthusiast herself and a champion at the Cowboy Action shooting competitions, where participants dress in costume, also runs a daycare center. The shooting range, where Livingston enthusiastically shot up a paper target, is just behind the colored playground slides.