Tools of Modern Gunmaking: Plastic and a 3-D Printer

A gun with a plastic lower receiver that was produced using a 3-D printer.

A man in Wisconsin viewed it as a technical challenge. Another, in New Hampshire, was looking to save some money. And in Texas, a third wanted to make a political point.

Chapman Baetzel, right, with his girlfriend, said that to save money he made his receiver on a 3-D printer he built from a kit.

The three may have had different motivations but their results were the same: each built a working gun that included a part made in plastic with a 3-D printer.

What they did was legal and, except for the technology and material used, not much different from what do-it-yourself gunsmiths have been doing for decades. But in the wake of the shootings in Newtown, Conn., and the intensified debate over gun control, their efforts, which began last summer, have stoked concerns that the inexpensive and increasingly popular printers and other digital fabrication tools might make access to weapons even easier.

“We now have 3-D printers that can manufacture firearms components in the basement,” said Representative Steve Israel, Democrat of New York. “It’s just a matter of time before a 3-D printer will produce a weapon capable of firing bullets.”

A 3-D printer builds an object layer by layer in three dimensions, usually in plastic. To effectively outlaw weapons made with them, Mr. Israel wants to extend an existing law, set to expire this year, that makes weapons that are undetectable by security scanners â€" like a printed all-plastic gun â€" illegal.

But there are also major technical obstacles to creating an entire gun on a 3-D printer, not the least of which is that a plastic gun would probably melt or explode upon firing a single bullet, making it about as likely to kill the gunman as the target.

In the meantime, Michael Guslick in Milwaukee, Chapman Baetzel in Dover, N.H., and Cody Wilson in Austin, Tex., did something much simpler and, for now, more effective. They printed the part of an AR-15 assault rifle called the lower receiver, the central piece that other parts are attached to. Then, using standard metal components, including the chamber and barrel â€" the parts that must be strong enough to withstand the intense pressure of a bullet firing â€" they assembled working guns.

In all, the three men, who have written about their efforts on the Web, have fired hundreds of rounds, although the plastic receivers eventually deform, crack or otherwise fail from heat and shock. But Mr. Wilson, for one, is working on a fourth-generation design that he says should be more durable.

A lower receiver is the only part of an AR-15 that, when bought, requires the filing of federal paperwork. But it is legal to make an AR-15 â€" and many other guns â€" for personal use as long as there is no intent to sell them. And if the lower receiver is homemade, no paperwork is required.

Amateur gunsmiths have made lower receivers for years, in metal, although the process requires a certain level of machining expertise. Inexpensive 3-D printers have grown in popularity â€" their rise has been compared with that of personal computers in the 1980s â€" in part because they are easy to use. It is not even necessary to know how to create the design files that instruct the device to print bit after bit of plastic to build the object, as there are files for tens of thousands of objects available on the Internet, created by other users and freely shared.

Still, some tinkering is usually required. Mr. Guslick, who works in information technology and describes himself as a hobbyist gunsmith, printed his receiver on a machine he bought online through Craigslist. He used a file and abrasive paper to make the piece fit properly, but over all the project was not much of a technical challenge. “Anybody could do this,” he said.

Mr. Baetzel, who made his receiver on a 3-D printer he built from a kit, said the part worked fine until he cracked it when bumping the gun while putting it in his car. He has since printed a replacement along with a modified grip and stock which, he said, has made the gun sturdier.

A version of this article appeared in print on January 30, 2013, on page A12 of the New York edition with the headline: Tools of Modern Gunmaking: Plastic and a 3-D Printer.