The TSA frequently shares images confiscated weapons on Instagram, but they tend to be pretty "old school": you see a lot of throwing stars, swords, and antique-looking firearms.

While these items are well worth keeping on the no-fly list, the agency shared a distinctly different and arguably more menacing threat in a recent post: a 3D-printed handgun with live rounds.

In a Tuesday blog post, Gizmodo took note of the discovery and pointed out that 3D-printed guns can skate by airport security metal detectors because they are are made of plastic or resin.

The gun was confiscated at the Reno, Nevada airport, according to the website 3Dprint.com. Authorities were unable to match its design to any files available online, so the passenger may have designed it personally.

The post exposes an unsettling loophole in how regulations fail to address 3D-printed guns.

Writing for Gizmodo back in 2015, Adam Clark Estes explained that regulating 3D-printed firearms presents quite the hornet's nest for lawmakers.

Firearms are a Second Amendment issue, while publishing instructions on how to make them falls under the First Amendment.

A 2013 law signed by President Barack Obama extended a 25-year-old ban on plastic guns, but did not impose regulations on 3D-printed weapons, according to Motherboard.

New York Congressman Steve Israel has advocated for a law to ban 3D-printed guns since 2013. His bill hasn't made any progress, even as the technology has advanced "from a few simple components to a full one-shot pistol to rifles and multi-shot revolvers," Wired reports.

In January, Rep. Israel announced that he will not seek re-election, and plans to work on "a new humorous book on the gun lobby" once he leaves office, the New York Times reports.

Some states and cities have passed laws to tackle the problem on a local basis.

In late July, California Governor Jerry Brown signed a law requiring 3D printed guns to be registered and anyone who makes a 3D printed gun to pass a background check, a move that ignited outrage from the NRA and various gun rights groups.

“Today’s action by Governor Brown shows how craven California’s despotic ruling class has become," Firearms Policy Coalition president Brandon Combs wrote in a statement. "The Legislature has abandoned the Constitution, representative government, and the People of California. I fully expect the People to respond in kind.”

Not all gun control groups are prioritizing the issue.

From Wired:

"But not every gun control group sees homemade or undetectable weapons as such a high priority. 'The notion that a mass shooter or a street criminal is going to buy a 3-D printer, download blueprints, and try a few test runs before producing their own gun is very unlikely,” says Ladd Everitt, the communications director for the Coalition to Stop Gun Violence. “It’s a hassle, when you can just buy a gun with zero accountability in this country.'"

[h/t Gizmodo]