Eighteen months after demonstrating that he could make a 3D-printed gun, Cody Wilson announced Wednesday that his nonprofit group, Defense Distributed, has now moved on to simplifying the process of manufacturing traditional metal guns.

Defense Distributed is now selling a $1,200 computer-numerically-controlled (CNC) mill—dubbed the "Ghost Gunner"—that can complete an unfinished lower receiver for an AR-15 semi-automatic rifle as part of a limited pre-order. While designed to mill an AR-15 lower, the CNC could theoretically mill anything of a similar size.

Wilson's new Ghost Gunner makes home gunsmithing faster, cheap and more portable than ever before.

Now, the total cost of semi-finished lower, a parts kit, an upper, a magazine, and the Ghost Gunner costs around $2,000—not a significant savings over buying the whole thing lock, stock, and barrel—but many hobbyists are excited at the opportunity. The price is expected to rise to at least $1,500 in 2015. As of this writing, Wilson had already sold 38 as part of that $1,200 pre-order.

The Ghost Gunner name is a jab at California State Senator Kevin De León, who introduced a bill that would have banned the sale, manufacture, purchase, and trafficking of untraceable "ghost guns" unless they were pre-registered with the Department of Justice through a serial number and gun owner background check. However, Gov. Jerry Brown vetoed the bill on Tuesday. (De León's office did not immediately respond to Ars' request for comment.)

"We're getting better at throwing back the nightmare scenario," Wilson, a self-described crypto-anarchist, said.

What exactly is a gun, after all?

The lower receiver part of a firearm is the crucial part that contains all of the gun's operating parts, including the trigger group and the magazine port. (Under American law, the lower is what's defined as the firearm itself.) The AR-15, the civilian version of the M-16 military assault rifle, is designed to be modular, meaning it can be assembled from different receivers, barrels, buttstocks, and other components, each with its own characteristics.

With a semi-finished lower, a parts kit, an upper, and a magazine, Wilson told Ars that anyone can hook up the mill to their computer and have a gun ready to fire in a short period of time.

"Our gold standard is: you're going to finish it in an hour," he said.

The United States Gun Control Act (GCA) of 1968 allows anyone to manufacture their own firearm without a license, but manufacturing such weaponry for sale or transfer does require a federal license.

As a way to get around that law, manufacturers can make a product that isn't technically a gun, but gets as close to the line as possible. The Ghost Gunner CNC mill requires that the buyer provide their own semi-finished lower, which is sometimes dubbed an "80 percent lower."

"The term 80 percent receiver comes from the seller, that's not a term that we use," a spokesman from the Bureau of Alcohol, Tobacco and Firearms (ATF) told Ars.

"That's a term from the seller or creator or the device that it's 80 percent of a finished receiver, therefore it is legal. That's not a determination we make."

In short, in the ATF's view, either something is a firearm or it isn't. And if it isn't, it can be sold without restriction.

Ain't no party like a build party

That metal piece is openly sold by various vendors, usually for under $100. Some of the vendors have received certification from the ATF that these 80 percent lowers are not, in fact, firearms. Wilson recommends 80 percent lowers made by Ares Armor, which has not received such a certification, and is currently embroiled in a lawsuit against the ATF.

"I'm extraordinarily happy that [Wilson] was able to get a product like this out to market and that he's as far along as he is," Dimitrios Karras, the CEO of Ares Armor, told Ars.

"It's what is needed in the community right now. The Second Amendment is consistently under attack. It's very important that people have the ability to be self-sufficient and to progress not regress."

Previously, milling would require renting time on a traditional large CNC (rather than a desktop version, such as this one). Some gun enthusiasts would participate in "build parties," where they would gather at a CNC to finish off their product. However, in early 2013, those on-site build parties were shut down by the ATF—but going to another location or doing it yourself to achieve the same ends is still within the law.

Or, anyone can mill an 80 percent lower by hand.

"If you were skilled it would take you two to three hours, unskilled it would have taken you a weekend," Karras said. "This is a way for people to maintain their privacy in the process of gun ownership."

Gun-rights advocates lauded the release, while the Brady Campaign to Prevent Gun Violence did not immediately respond to Ars' request for comment.

"Innovation will continue to rule the day," Brandon Combs, the president of the California Association of Federal Firearms Licensees, told Ars.

"People have been building firearms at home for many years—centuries, really. You cannot regulate innovation out of existence. At one point there was a web forum where a poster described how he built an AK-47 with a garden shovel as the base for the receiver. There's no end to creativity—the real question is the mens rea—are we talking about people doing good or doing bad? Overwhelmly, gun owners in the US use guns for law-abiding purposes in a safe manner."