Though a federal judge has temporarily blocked the dissemination of blueprints showing how to make guns using 3-D printers, it remains legal for people to make their own firearms at home without a license — a relatively rare practice but one that the government cannot fully monitor.

Federal law allows people who are not prohibited from owning firearms to manufacture them for personal use. Certain types of guns, including those with short barrels, require a tax payment and approval from the Bureau of Alcohol, Tobacco, Firearms and Explosives. A license is required to make guns for sale or distribution.

It is unclear how many DIY guns are made each year, because many of them are not registered and most parts do not carry serial numbers that would enable tracking.

Gun enthusiasts say making firearms at home is a hobby much like building a car engine, a way to learn about the intricacies and mechanisms of the machine rather than creating something for regular use. Gun-control advocates say the ability to make guns is a major legal loophole that could allow for people who cannot legally own a gun to circumvent a background check and get a firearm.

“There’s nothing in federal law that prohibits private parties from making their own firearms as long as they’re not prohibited people in the first place, and that’s long been the case,” said Nicholas Johnson, a professor of law at Fordham University. “The basic idea of home manufacturing for personal use is pretty uncontroversial, or has been.”

It is illegal to make a gun that cannot be detected by a metal detector or X-ray machine. Fully plastic guns also are illegal under an amendment to the Gun Control Act of 1968, making it possible that some 3-D-printed guns that do not contain metal could violate the law. People also are prohibited from making a non-sporting semiautomatic rifle or shotgun from 10 or more imported parts.

Home gun manufacturing happens in various ways. Kits that have all the components to make a gun are available online, typically costing a few hundred dollars. It is also possible for a trained machinist to make a gun from scratch. One can buy a gun receiver, which is akin to buying a gun and requires a background check, and make it work by adding parts. Some kits contain what are known as 80 percent receivers, which is a block of aluminum in the shape of a lower receiver. It must be assembled and does not qualify as a firearm purchase under federal law.

“People like to learn. I think a lot of people like to do things themselves. People like to do home projects and change stuff around on their house; why wouldn’t they want to do the same thing with their vehicles or their firearms?” said Brandon Combs, president of the Firearms Policy Coalition. Combs’s organization created a website that shows instructions for how to build various guns, including an AR-15 assault-style rifle. The group that created the 3-D blueprint released it online before this week’s court order, and its specs remain on the website created by the Firearms Policy Coalition.

Combs said the allure of making guns at home becomes stronger when stricter gun laws are enacted.

“The more gun control gets passed, the more popularity there’s been for these types of home-built firearms and do-it-yourself projects,” he said. “What’s the rational basis for telling people who are not prohibited that they cannot learn how to do stuff?”

Jim Irvine, president of the Buckeye Firearms Association in Ohio, said he and two friends made AR-15s after buying component parts and watching a video online.

“It’s like a kid building a model,” he said, noting that it was fun building the gun and that it gave him a further appreciation for the weapon and its craftsmanship. But he would rather purchase a firearm to use.

“I could watch a YouTube video on how to do a surgery, but if it’s somebody I care about, I’m not going to try this. I’m going to pay a professional. It’s the same thing if I want a reliable gun, I’m going to pay a professional.”

Other gun enthusiasts wonder why people would try to make a gun at home when they could buy one.

“I don’t know anybody in their right mind or otherwise who would build a gun,” said Alice Tripp, legislative director of the Texas State Rifle Association. “If it’s not done correctly, it won’t work. It’s not something that is going to be on the DIY Network.”

But some believe the ability for anyone to manufacture a gun makes it much easier for people who are prohibited from owning guns to acquire them. In 2013, a man killed five people in Santa Monica, Calif., using a gun he had built. And last year, a man in Rancho Tehama Reserve, Calif., who was prohibited from owning guns used at least two semiautomatic rifles built at home to kill his wife and four others.

Such guns also are known as “ghost guns” because they are not traceable. A California law requiring homemade guns to be reported to authorities went into effect on July 1.

Los Angeles law enforcement officials have said gang members there have been acquiring more guns made at home as it becomes more difficult to buy firearms legally.

The New Jersey attorney general has demanded that companies stop selling and marketing ghost guns and their component parts in the state. And a bill was introduced in the New York State Assembly this week requiring the registration of homemade guns.

“It’s a loophole that exists only because it used to be very difficult to do this before we had modern technology and there wasn’t a safety risk from DIY gunmakers,” said Jonas Oransky, the legal director for Everytown for Gun Safety. “Given the current technology, it now is really an absurd problem to have, where you can just make your own gun and skip the considerable framework of federal gun laws.”