Travis Lerol prints a lower receiver for an AR-15 at his home in Glen Burnie, Md. The printer uses plastic instead of ink, and the process takes about 10 hours. (Whitney Shefte/The Washington Post)

Twenty minutes into his State of the Union address last week, President Obama entered the realm of uber-geekery — three-dimensional printing. The magical devices capable of printing prosthetics, violins and even aircraft parts have the potential, the president said, “to revolutionize the way we make almost everything.”

Forty miles away from the Capitol, in Glen Burnie, Md., Travis Lerol is proving Obama’s point — with guns.

In a spare bedroom, where an AR-15 rifle leans against the wall, Lerol is using a 3-D printer no larger than an espresso machine to make plastic rifle parts and ammunition magazines in between tea sets and chess pieces. The parts print, layer over layer, creating objects like an ink-jet printer etches words.

The 30-year-old software engineer said he has no plans to print anything outlawed by the government. But like many other gun owners, he is nervous that the push for gun control in the wake of the Sandy Hook Elementary School massacre will infringe on his Second Amendment rights.

Three-dimensional printers offer a potentially easy way around restrictions and registrations — a source of growing consternation among gun-control advocates and some allies in Congress.

Travis Lerol holds an AR-15 assault rifle that contains a bullet clip made of ABS (Acrylonitrile Butadiene Styrene) plastic that was constructed by his 3D printer at his home on Feb. 12. (Jahi Chikwendiu/The Washington Post)

“There’s really no one controlling what you do in your own home,” Lerol said.

Though printing guns is a craft still in its infancy — Lerol hasn’t tested his parts yet at a gun range — technology experts, gun rights proponents and gun safety advocates say the specter of printable firearms and ammunition magazines poses a challenge for Obama and lawmakers as they craft sweeping gun-control legislation.

One controversial idea, pushed by Sen. Dianne Feinstein (D-Calif.), is to outlaw high-capacity magazines. But some proponents of 3-D printed guns have already made high-grade plastic replicas.

“Obviously, that has to be one of her nightmares,” said Larry Pratt, executive director of Gun Owners of America, a lobbying group opposed to additional restrictions. “If her ban was to pass and this technology moves beyond its infancy, Dianne Feinstein is going to have a bit of a challenge.”

Feinstein’s proposed legislation, which would also ban AR-15s, restricts manufacturing of such items by anyone in the country, said a spokesman for the senator.

But 3D-printing experts say that logic is dated and misses the point of the technology. Making guns for personal use has been legal for decades, but doing so has required machining know-how and a variety of parts. With 3-D printers, users download blueprints from the Internet, feed them into the machine, wait several hours and voila.

“Restrictions are difficult to enforce in a world where anybody can make anything,” said Hod Lipson, a 3-D printing expert at Cornell University and co-author of the new book, “Fabricated: The New World of 3D Printing.” “Talking about old-fashioned control will be very ineffective.”

It is unclear how many people are trying to print their own gun parts and magazines. But Cody Wilson, a University of Texas law student who is leading the ideological and technical campaign for 3-D printed guns through an organization called Defense Distributed, said blueprints have been downloaded hundreds of thousands of times from his group’s Web site.

“People all over the world are downloading this stuff all the time — way more people than actually have 3-D printers,” he said. “This is hot stuff on the Internet now.”

Wilson and a friend founded Defense Distributed last February while looking for a “post-political” project to challenge governmental scrutiny and regulations. He speaks of “prohibitionist regimes” and anarchistic urges and challenging “democratic control.” Though he shot guns as a Boy Scout, Wilson doesn’t consider himself a gun person. He doesn’t consider himself a tech geek either. His motivations, he said, are ideological and go way beyond the Second Amendment.

“This is a symbolic challenge to a system that says we can see everything, regulate everything,” he said. “I say, ‘Oh really?’ My challenge is: Regulate this. I hope with that challenge we create such an insurmountable problem that the mere effort of trying to regulate this explodes any regulatory regime.”

Wilson’s group has posted several videos to YouTube of AR-15s firing rounds with 3-D printed high-capacity magazines and lower receivers, the part that includes the firing mechanism and is the only regulated portion of the gun if it’s bought over the counter. Wilson’s parts are made from high-grade polymer and retrofitted to the bodies of existing weapons. The receivers are made able to fire by adding over-the-counter springs, pins and a trigger.

In one recent video, Wilson fires dozens of rounds from an M-16 using a 3-D printed high-capacity magazine. “How’s that national conversation going?” he asks.

Defense Distributed also runs a Web site called Defcad, where anyone can download gun designs and trade tips. The other day, a user posted this question to a discussion board on the site: “I know nothing of 3d printers. I can tell there are a few different types of materials to print and some appear to be easier to break than others. What printer and material is the best for printing a receiver and mags?”

Lerol, working in his spare bedroom, is using a $1,300 machine called the Cube, which is made by a division of 3D Systems, a large publicly traded manufacturer of consumer and industrial 3-D printing machines. The cheaper, consumer versions of 3-D printers like the one Lerol uses are only capable of printing with plastics, while more expensive, industrial-scale machines can print sturdier materials such as high-grade polymers.

Experts expect printer prices to fall as part of the normal technology curve. (Think about the price of flat screen TVs five years ago. Or a computer two decades ago.)

And that makes Lipson, the Cornell expert, nervous because cheaper machines could help people make cheap guns for one-time use.

“The threat is not of 3-D printing military-grade weapon components from standard blueprints on industrial 3-D printers,” Lipson said. “The challenge is that [do-it-yourself] 3D printers can be used by anyone to print rogue, disposable and shoddy guns that could be used to fire a few rounds, then be recycled into a flower vase.”

Though Lerol acknowledges how easy these machines make it to get around regulations, his motivations, he said, are benign. He is a tinkerer, he likes guns and he likes messing around the house. He insists he has no interest in flouting whatever restrictions might win approval, but gun-control advocates and some legislators worry that not everyone’s motivations will be so pure.

“It’s not necessarily the technology, it’s the ideology,” said Joshua Horwitz, the executive director of Coalition to Stop Gun Violence. “If this insurrectionist philosophy was to gain traction, people will normalize this behavior.”

Legislators pushing for additional gun control say that 3-D printing is on their radars, but it’s unclear whether they can do anything about it.

Rep. Jim Langevin (D-R.I.), a member of the House Gun Violence Prevention Task Force, said in a statement that he has “raised concerns” about 3-D printing to task force representatives but that “more information is necessary to properly address this complex, yet still nascent issue.” He adds that he would “explore appropriate policy solutions to ensure it is not utilized in a manner that poses a threat to public safety.”

Rep. Steve Israel (D-N.Y.) wants to renew a law he thinks could protect the country from the threat of 3-D printed guns: the Undetectable Firearms Act. Passed in 1988, the law prohibits manufacturing or possessing a gun that can’t be detected by airport security scanners. The law expires at the end of the year. Israel also wants to update it to include plastic ammunition magazines.

“I believe that 3-D printers can change the world for the better,” Israel said. “What I am concerned with is the proliferation of weapons and weapons components made by 3-D printers which can be easily brought onto airplanes and other high-security environments and do grave damage.”

Israel thinks 3-D printed guns haven’t received the scrutiny they deserve.

“The technology is proceeding so rapidly that when I talk about three-dimensional guns, people think I’m talking about a ‘Star Trek’ plot,” he said. “When I show them how easy it is to make, most people are shocked. When I tell them the law that would stop these plastic guns from getting onto planes is expiring in just a few months, people are appalled.”

Three-dimensional printer companies are also worried. After the Sandy Hook shooting in December, MakerBot removed gun designs from a Web site of downloadable blueprints it maintains for users of its 3-D printers. Stratasys, another major 3-D printing company, leased a machine to Wilson last year, but company officials confiscated it after learning of Wilson’s plans.

“We believe Mr. Wilson intended to use Stratasys property to produce a weapon that is illegal according to the Undetectable Firearms Act of 1988,” the company said in a statement. “It is the legal responsibility of Stratasys not to knowingly allow its property to be used for illegal purposes.”

3D Systems, the company that makes Lerol’s machine, has also closely been monitoring the gun developments. Abe N. Reichental, the company’s chief executive, said he is open to working with members of the industry and legislators to restrict certain shapes from being printed.

“We don’t want to prevent printing anything that is legal and proper,” he said. “But we want to be responsible. We want to do good. We want to be a force that helps shape the goodness of this technology and its use.”

But even if companies somehow restricted printing certain shapes from their machines, Lipson, the 3-D printing expert from Cornell, said that wouldn’t do much good because there are open-source, self-built printers on the market that aren’t connected to the mainstream printing community.

He suggests one way to prevent dangerous, illegal usage of 3-D printers is to better control gunpowder, an idea that has come up in gun control in the past.

“What we really need is different solutions,” he said. “Weapons will be difficult to control.”