A University of Texas at Austin law student has demonstrated to the world that any ambitious tinkerer can make a handgun almost entirely out of 3-D printed parts. Cody Wilson’s revelation is not likely to lead to an arsenal of plastic zip guns anytime soon, but it does raise a number of hairy questions about a technology that, until now, has been highly touted as central to the future of manufacturing in the U.S.

Images and video of Wilson posing with and firing his “Liberator” handgun have made the rounds on the Internet in recent days. It’s a stark contrast to the image that 3-D printing, or “additive manufacturing,” proponents have pursued thus far, where the world benefits from robotic prosthetics, replacement hips and other biomedical wonders manufactured layer by layer out of molten plastic or metal, as dictated by a CAD (computer-aided design) file.

Wilson’s gun consists of 15 parts assembled after being printed individually in a Stratasys Dimension SST machine out of white ABS plastic—a polymer made from the chemical compounds acrylonitrile, butadiene and styrene. Only the gun’s firing pin (a common nail) and an obligatory piece of steel embedded in the handle—so that it does not violate the Undetectable Firearms Act (pdf)—are metal. Wilson has made the design files needed to create the Liberator—that fires standard handgun rounds—available as a free download for anyone interested in replicating his work.

Wilson positions himself as a protector of civil liberties—in particular “popular access to arms”—and has founded a nonprofit called Defense Distributed to further this goal. His libertarian views are not unlike those of free, open-source software advocates or hackers who take down Web sites and pick apart popular software like Windows to prove they are not as secure as they appear—except for the small detail that he wants to empower people to make devices that can harm or kill other people. (He’s also published blueprints for 3-D printing part of an AR-15 semiautomatic rifle.)

Technically speaking, Wilson’s so-called “Wiki Weapon” pushes the boundaries of 3-D printing capabilities, especially those of lower-end systems not able to work with anything stronger or more durable than ABS plastic. Although the Liberator currently fires only a single shot, better materials as well as improved designs and post-processing techniques might ultimately lead to a weapon that can shoot multiple rounds without breaking down.

To learn more about the potential impact of Wilson’s work on the world of 3-D printing, Scientific American spoke with Ryan Wicker, director of the University of Texas at El Paso’s W. M. Keck Center for 3-D Innovation. Wicker shared his thoughts about Wilson’s invention, the technical challenges of making a 3-D printed gun and the reality that the unbridled creativity promoted by 3-D printing was destined to take a darker turn.

[An edited transcript of the interview follows.]

What was your reaction when you learned that someone had printed nearly all of the components needed to assemble a handgun using a 3-D printer?

This story has been developing for months, if not years, so it was pretty anticlimactic. I probably first became aware of what [Wilson] has been doing when Stratasys went in and confiscated the printer they leased to him [in October. I have been hearing for years about people using 3-D printers to make parts for guns. In the evolution of 3-D printing it’s certainly natural for things like this to happen.

Are there specific challenges to making a working firearm using 3-D printed parts?

Building the parts with a high level of dimensional accuracy would be one challenge and the material performance would be another. A firearm experiences a high-energy impulse in the chamber, where the gun components start off at ambient conditions but are subjected very quickly to higher temperatures and pressures. This sudden change can compromise the structural integrity of the gun, even possibly making it explode.

What is the significance of Wilson making most of his gun parts out of ABS plastic?

ABS is an inexpensive polymer typically used by the type of 3-D printer that he used. There are plastics that are stronger, more durable and perform much better than ABS, but those higher-end materials require higher-end machines than what he had.

Why is ABS the standard plastic for lower-end systems?

ABS is just a commodity, a commonly used plastic that the automotive industry has used for years to create injection-molded parts. Different 3-D printing systems work differently, but [Wilson’s] uses an extrusion-based process that’s analogous to a hot-glue gun. ABS’s extrusion temperature [the point at which the polymer starts to deform and can be squeezed out into layers] is lower than other, more capable plastics. It doesn’t require a more expensive system that can [operate at] higher temperatures.

Why not use a more durable plastic?

Stratasys offers a more expensive plastic called Ultem, which potentially would be a better performer than ABS for this application. But you can’t print this type of high-end material using the low-end [$20,000] industrial printer that [Wilson] used. You need a high-end machine that costs anywhere between $100,000 and $400,000 to be able to use those better plastics. Although it’s not possible now, that doesn’t mean someone couldn’t develop the capability to work with better plastics on low-end systems.

Other than the materials that can be used, what limitations do lower-end 3-D printers have at this time?

Another limitation is accuracy. These machines don’t have the temperature control of higher-end systems, and consequently the dimensional accuracies suffer. The more expensive industrial systems take into account how much a part will change as it goes through the process of being made. Better temperature control enables a printer to better adjust for changes in the material as it is layered, solidifies and shrinks. If you don’t take those changes into account, some layers might be farther apart, creating voids that prevent the finished product from being as strong as it could be.

All of these things can be overcome. There are lots of people working in their homes on inexpensive desktop systems [like those MakerBot produces] who are going to be geeky, experimenting and optimizing their systems. They’ll write their own code and figure out how to compensate for their equipment and materials. That’s what my students do. There is some knowledge that you have to develop to use these systems optimally.

As inventors develop this knowledge, are there concerns that more of them will experiment with 3-D printed weapons?

3-D printing is not the only enabling technology here. 3-D printers may be a little less complicated to use than [some computer numerical control (CNC) systems that manufacturers use to make tools], but you still can buy a CNC machine today and use that to build weapons. In fact, I would be much more scared of people who have expertise in machine shops [making weapons] than I would of someone using a 3-D printer.

And, even if you don’t print the parts for the weapons yourself, there’s an entire industry that makes parts on demand today using 3-D printing. You can upload your file online without even speaking with anyone and pay for it with your credit card.

How soon will higher-end 3-D printers capable of using better materials become affordable for hobbyists and inventors?

I don’t know how much the cost can come down for some high-end systems because they are big machines and they use more expensive industrial components, which limits how much the price can be reduced. And the price of high-end systems may not be the limiting factor for hobbyists because they can take a desktop system [like those made by MakerBot] and supercharge it, and there’s no technical reason you couldn’t use it to print a weapon.

How would you supercharge a desktop 3-D printer to give it that capability?

I may enclose it so that I can reach higher temperatures and work with [stronger, more durable] materials. I might also do this by modifying the printer’s heater to make the printhead hotter.

People are less likely to modify an industrial system because companies like Stratasys don’t give you access to their printer’s source code. MakerBot and other desktop printer–makers do. That means I can write my own code to change things on these lower-end systems but I can’t [change] that on a Stratasys system. Even the materials used by industrial systems are controlled. A canister of material used in a Stratasys printer even has a microchip that knows what and how much material it contains.

What impact will Wilson’s experiment have on 3-D printing?

It concerns me a little, but I think this type of project was inevitable. We would all like these technologies to be used for the benefit of society, and I believe these benefits far outweigh the risks. There are lots of wonderful examples—customized hearing aids, 3-D printed electronics and even shoes as well as [efforts to print artificial human] organs. The government will ultimately decide whether the technology should be regulated, but I see these technologies completely disrupting the way we make products, and bringing innovative, entrepreneurial manufacturing work back to the U.S. We’ve traveled too far down the road to turn back at this point. With these technologies, the future is limited only by one’s imagination.

In mid-April, Kansas passed a law asserting that federal gun regulations do not apply to guns made and owned in Kansas. Under the law, Kansans could manufacture and sell semi-automatic weapons in-state without a federal license or any federal oversight.

Kansas’ “Second Amendment Protection Act” backs up its states’ rights claims with a penalty aimed at federal agents: When dealing with “Made in Kansas” guns, any attempt to enforce federal law is now a felony. Bills similar to Kansas’ law have been introduced in at least 37 other states. An even broader bill is on the desk of Alaska Gov. Sean Parnell. That bill would exempt any gun owned by an Alaskan from federal regulation. In Missouri, a bill declaring federal gun laws “null and void” passed by an overwhelming majority in the state house, and is headed for debate in the senate.

Mobilizing the pre-Civil-War doctrine of “nullification,” these bills assert that Congress has overstepped its ability to regulate guns — and that states, not the Supreme Court, have the ultimate authority to decide whether a law is constitutional or not.

The head of the Kansas’s State Rifle Association, an affiliate of the National Rifle Association, says she put the bill together and found it a sponsor. While the NRA regularly lauds passages of states’ gun-rights laws, it stayed silent on Kansas’ law, and, so far, has kept a low profile on nullification. (The group did not respond to our requests for comment.)

Many observers see nullification bills as pure political theater, “the ultimate triumph of symbolism over substance,” as UCLA law Professor Adam Winkler put it.  He said he doubts the laws will ever be enforced, and, if they are, expects them to be struck down by the courts.

Winkler and others say nullification laws violate the Constitution, which makes federal law “the supreme law of the land … anything in the Constitution or laws of any State to the contrary notwithstanding.” Indeed, U.S. Attorney General Eric Holder wrote a letter last week to Kansas Gov. Sam Brownback, asserting that Kansas’ law is “unconstitutional.” (Brownback, who signed the bill into law, did not immediately respond to our requests for comment.)

But the growing number of such bills -- which have passed by large majorities in at least one chamber of seven state legislatures -- highlight the challenge gun control advocates face in their attempt to fight for gun regulation at the state level.

It also shows how nullification is fast becoming a mainstream option for state politicians. In Pennsylvania, 76 state legislators signed on to sponsor a measure that would invalidate any new federal ban of certain weapons or ammunition. The bill would impose a minimum penalty of one year in prison for federal agents who attempt to enforce any new law.

Supporters of nullification are not simply frustrated at what they see as congressional and presidential overreach. During a hearing about one of the nullification bills she had introduced, Tennessee State Sen. Mae Beavers called the Supreme Court a “dictatorship.”

“You think that the Supreme Court is the ultimate arbiter of any of these laws. I don’t believe that. I don’t believe it was ever granted the authority under the Constitution,” Beavers was quoted as saying in The Tennessean. (Reached by phone, she asked to comment later, then did not respond to further requests.)

The Supreme Court rejected nullification in 1958, after Southern states tried to use the concept to avoid desegregating public schools. “No state legislator or executive or judicial officer can war against the Constitution without violating his solemn oath to support it,” the Court ruled.

Winkler, the UCLA law professor, said that even though the nullification trend was likely to be ineffectual, “It represents a strong, powerful opposition to our government.”

The concept of nullification has had a resurgence since the beginning of President Obama’s administration. More than a dozen states have introduced bills to nullify Obamacare.

The Tenth Amendment Center, a group that advocates nullification as the solution to a range of policy issues, from marijuana legalization to Obamacare, publishes model gun nullification language. The center has little direct contact with state legislators, Michael Boldin, the center’s founder, said.

The roots of guns law nullification trace back nearly a decade.

In 2004, Montana gun rights activist Gary Marbut drafted a bill stating that any guns manufactured and retained in Montana are not part of interstate commerce, and thus are exempt from federal regulation. The bill failed twice, but it became law in 2009 after Republicans took control of the statehouse. By Marbut’s count, at least eight states soon enacted “clones” of the Montana law. (Those laws don’t go quite as far as the more recent nullification legislation. For instance, most of them don’t make it a crime to enforce federal law.)

The federal Bureau of Alcohol, Tobacco and Firearms responded to the earlier laws with letters to local firearms dealers explaining that federal laws and regulations “continue to apply.”

The day the Montana law went into effect, Marbut filed a lawsuit in federal court asserting the right to manufacture weapons in the state without a federal license. The suit, now before the Ninth Circuit Court of Appeals, has been backed by a large group of supporters, including Gun Owners of America, the Second Amendment Foundation, the Cato Institute, the Goldwater Institute, and a group of nine attorneys general, some of them from states that had passed their own versions of the Montana law.

Representatives of Goldwater and the Cato Institute said they see the case as not primarily about guns. Instead, they say, it’s meant to persuade the Supreme Court to rollback the Congress’ power to regulate commerce within a state.

“The likelihood of victory is low,” said Trevor Burrus, a research fellow at the Cato Institute’s Center for Constitutional Studies.

The latest set of bills — including Kansas’ new law — represent a far broader and more aggressive challenge to federal law. Even conservative organizations have been skeptical of the trend.

“A state law that criminalizes federal activity — I would oppose that as both imprudent and wrong,” Burrus said. The Cato Institute’s chairman wrote an op-ed this spring arguing this kind of nullification is invalid.

Goldwater Institute’s Nick Dranias, a constitutional expert, said the term “nullification” is sometimes applied to legitimate attempts to exert state sovereignty, “and sometimes it is essentially lawless civil disobedience.”

States should only pass laws challenging federal power "when there is a reasonable legal argument for sustaining them," he said. And the penalty for enforcing federal law in "hard cases" should be "a misdemeanor at most."

The Heritage Foundation, a conservative research group, released a “fact sheet” last year titled “Nullification: Unlawful and Unconstitutional.” (The fact sheet does not address guns in particular.)

The Montana activist whose helped inspired the nullification movement Kansas is also a bit skeptical. While he simply chose to challenge the federal government’s commerce power, Kansas is “bucking federal power more generally,” he said.

“I think, maybe tactically, they may have gone a little further than they needed to,” Marbut said.

Though he supports the principles behind the Kansas law, “I don’t know how much of that they can uphold when it gets to the courts.”

But Marbut hopes that the rapid spread of gun law nullification bills across the country will encourage the Supreme Court to hear his case.

“I see the tide moving our way,” Marbut said. “I think the Supreme Court has figured out that the people of America are gathering their torches and pitchforks and it’s time to settle things down by reeling in the federal giant.”

A spokeswoman for Alaska Gov. Parnell, who has not either approved or vetoed the state’s nullification bill, said last month that “he is supportive of it.” But, she added, “The bill (as with all bills that pass) is currently undergoing a thorough review by the Department of Law.”

In Kansas, Patricia Stoneking, the president of Kansas State Rifle Association, said she was recommending that Kansans not start manufacturing guns under the new law until its legal status has been clarified.

Even if Kansas’ law ends up being struck down in court, “We actually are not going to roll over and play dead and say, ‘Oh, no, shame on us,’” Stoneking said. “The fight will not be over.”