Travis Lerol holds an AR-15 assault rifle along with a rifle’s lower receiver made of ABS (Acrylonitrile Butadiene Styrene) plastic that was constructed by his 3D printer at his home in Glen Burnie, Md. (Jahi Chikwendiu/The Washington Post)

Federal law enforcement officials are increasingly concerned about the public-safety threats posed by plastic handguns made with 3-D printers because they can potentially slip past metal detectors and are capable of firing lethal rounds.

At a media briefing Wednesday, senior officials of the Bureau of Alcohol, Tobacco, Firearms and Explosives said they had built and tested the Liberator, a printed handgun designed by Defense Distributed, a Texas organization. Cody Wilson, its co-founder, is a former law student leading a campaign for do-it-yourself firearms.

In one test, ATF officials fired eight rounds from the Liberator. Other tests and simulations showed that the weapon was capable of firing with enough power to injure vital organs.

The Liberator’s designs were downloaded more than 100,000 times in just two days before federal officials demanded their removal in May. The risk, officials said, is not that street criminals will use printed weapons in their day-to-day operations. Rather, ATF officials are concerned about individuals slipping plastic guns past metal detectors and into schools, sporting events or government offices.

Depending on the sensitivity of a metal detector, a bullet might not be enough to set it off. Only X-ray machines could spot the handgun itself, and in many public places they aren’t available.

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)

“There are ways that this can potentially create a huge problem for the American public,” said Richard Marianos, an assistant ATF director.

The ATF’s public education push comes as a law banning undetectable firearms is set to expire early next month. Rep. Steve Israel (D-N.Y.) is pushing a bill to reauthorize and update the law to account for 3-D printing technology. ATF officials, he said, have consulted on his measure, but it’s stuck in committee and its prospects appear dim. There is a similar effort in the Senate.

Meanwhile, the world of printed guns is evolving rapidly.

This month, Solid Concepts , a California manufacturing company, said it had successfully printed and fired a metal handgun. Although machines capable of printing metal are affordable only in industrial or commercial settings, experts say the technology will eventually trickle down to consumers, who are already able to purchase plastic printers at affordable prices.

“There are people who say 3-D printing is a fad and it’s going to go away, but it’s not,” said Hod Lipson, a 3-D printing expert at Cornell University and co-author of “Fabricated: The New World of 3-D Printing.” “You can make anything this way that you can make the old way.”

Anything, so far, has included aerospace parts, medical devices, consumer goods — and now handguns. The technology, which prints objects layer by layer much like an ink-jet printer, offers an end run not just around restrictions and regulations controlling the distribution of firearms — a subject of emotional debate around the country — but also the devices that detect them in public.

“It is something that we’ve never ever seen before,” Marianos said. He said the ATF’s Liberator handgun “can be manufactured in a warehouse, a garage. It’s made of polymer plastic and it does create a public-safety concern for the American public because it can defeat metal detection.”

Wilson, the gun’s creator, bristled at the idea that the Liberator was as dangerous as ATF officials say. The gun, he said, was intended more as an “interesting visible symbol and a locus for discussion.”

“I don’t share their concern,” said Wilson, who has a federal license to make firearms. “It’s an extremely impractical firearm. It misfires constantly. It’s almost completely useless. If someone wants to assassinate someone, they are going to use a more reliable firearm than that.”

But Israel, the New York congressman, is concerned.

He said he’s making a “last-ditch effort” to renew and update the law, which currently prohibits manufacturing or possessing a gun that can’t be detected by typical airport security scanners. Asked whether such a law mattered, given that it would not be able to control what someone built in their own garage, Israel said, “You could say that about drugs, about alcohol, about just about any law.”

“It would be unfathomable to me if we are not able to renew this law right now,” he said.