Thursday, March 14, 2013

The Open-Source 3D-Printed Gun

An interesting experiment in democracy is underway. Texas gunsmith and crypto-anarchist Cody Wilson is spearheading an effort to design, and open-source the plans for, the first 3D-printable gun. Earlier this month, Wilson's nonprofit organization, Defense Distributed, released a video showing a semi-automatic rifle firing off over 600 rounds with a printed plastic lower receiver.

I'm not a firearms enthusiast, but I'm a democracy enthusiast and an admirer of the crypto-anarchist style (things like Wikileaks), so this particular experiment in 1st and 2nd Amendment rights has me captivated, not the less so because Mr. Wilson himself is a law student.

I admit a certain fascination with the technological challenges presented by 3D gun-printing. The common presumption seems to be that a plastic gun will never be practicable (because a plastic barrel will never be able to withstand the temperatures and pressures achieved in conventional firearms operation), hence we needn't fear that the Cody Wilsons of the world will get very far in their quest for a 3D-printed weapon. We can reject that notion outright, it seems to me. Wilson will eventually succeed. The only question is how much technological innovation he'll have to bring to bear on the problem.

There's a long history to improvisational firearms (zip guns and such) in this country, and the fact is, if all you want to do is discharge a store-bought 9mm round from a tube, you can do so with $2 worth of off-the-shelf parts today (see for demo).

Cody Wilson's effort to create a printable gun is a technologically naive approach, in the sense that Wilson has chosen to replicate an existing design in plastic, rather than look at this as a clean-sheet-of-paper problem. I know nothing about guns, yet it seems obvious to me that any kind of firearm is a complete system that requires more than a sum-of-the-parts approach. If the goal is to deliver a conventional bullet of a certain caliber out of the end of a barrel at a certain muzzle velocity, it seems to me you'd want to design the gun from the barrel back rather than from the stock up, so to speak.

This AR15 lower receiver was printed using an
old-school Stratsys 3D printer and $30 worth of resin.
Having said this, I have zero doubt that a plastic barrel can be developed to fire a standard round of one sort or another. The question is whether such a barrel can do it more than one time.

A precedent for what Wilson is doing exists in the attempts to make a plastic car engine. Polimotor Research took the bottom-up approach when it made its famed plastic engine for Ford in the 1980s. It started with "bottom end" parts (oil pan, block, valve covers, etc.), progressing to connecting rods, pushrods, etc., but then hit the wall (technologically) when it got to the high-temperature components: pistons, cylinder liners, and valves, all of which had to remain metallic. I foresee something similar happening with the Wilson gun. When it comes to designing a plastic barrel that can accommodate a conventional round, Wilson will run into an impedance mismatch (so to speak) that will require some original thinking.

Increasing the barrel-wall thickness (probably to an inch or more) may well keep the barrel from shattering, but the question is what the inside of the barrel is going to look like after pressures of 20,000+ psi and temperatures of several thousand degrees Fahrenheit. (Note: Had Wilson decided to clone something simpler, like a 38 Smith & Wesson, the max pressure would be only 14,500 psi. See this chart.) These pressures and temperatures exist for only a fraction of a second, and only in the first inch or so of bullet travel, so perhaps Wilson can design a multi-part barrel in which the first two inches are metal, or in which the first two-inch segment is a disposable plastic piece (replaced after every round). Or perhaps Wilson can produce an innovation in barrel design that, by clever use of gas plenums and pneumatic oscillator effects, shapes the pressure and temperature curves exactly as needed, in operation. If Wilson were to design his own round, further innovations could be attempted, but I'm assuming Wilson's goal is to produce a gun that fires off-the-shelf ammunition. That certainly seems to be what he's after.

Bottom line, there are technical challenges ahead, requiring more than mere reverse engineering to solve. But I think the challenges can be overcome.

As for the non-technical challenges (e.g., to 1st and 2nd Amendment law), Wilson is doing us a service, I think, by accelerating the debate on guns and gun laws in this country. What will it mean to be able to "print" your own gun? Will the gun-control debate turn into a printer-control debate? Will gun laws become ammunition laws? (Clearly, you won't be able to 3D-print gunpowder. Wilson's gun needs real ammo.) Will we be any worse off, as a society, when anyone with a printer can print handguns and semi-automatic weapons? Or are we already so saturated  with firearms that it won't matter?

One wonders what the Founding Fathers would have written, in place of the Second Amendment, if they had known about 3D printer technology. Perhaps: "The right of the people to keep and bear printers shall not be infringed"?