Many active users of the printing technology are skeptical about the extent of the real threat posed by 3-D firearms. A sampling of discussion forums of 3-D enthusiasts finds widespread cynicism about the capabilities of such weapons.

“Three-D printing a gun or a knife is akin to building a car out of cheese — it’s just not going to work,” wrote someone posting as “thejollygrimreaper” on the RepRap forum, one of the biggest 3-D-printing online communities.

Another member of the same forum, who identified himself as Markus Hitter, 48, an engineering consultant from Germany, said he did not consider 3-D-printed guns to be a public threat. Still, he acknowledged in an e-mail exchange that “certainly some gun nuts will try — using the quite modest material properties of 3-D printing.”

Although the technology, also called additive manufacturing, has been around as an industrial process since the 1980s, it has only recently gained broader currency with the arrival of affordable consumer-level printers. But the actual number in use is still relatively tiny. According to Wohlers Associates, a 3-D printing research firm in Fort Collins, Colo., a total of 35,508 personal printers were sold worldwide last year, although that was up nearly 50 percent from 2011. Most of these machines were sold to hobbyists, do-it-yourselfers, engineering students and educational institutions, according to Terry Wohlers, the firm’s president.

A RepRap forum member identifying himself as a 21-year-old Finnish student from Tampere said he succeeded in printing a working gun and in testing it. Since he considers his own actions to be illegal under the strict gun laws in Finland, he declined to reveal his name in a message exchange.

It was “for educational purposes and out of curiosity” that the student said he downloaded the original Liberator model in early May, shortly before the American government ordered the files taken down. He said he made the weapon on a friend’s 3-D printer and fired it. “The gun’s receiver got a crack after just one shot,” he said, referring to the firing chamber. “No sane person would fire the gun again.”