Franklin's famous apothegm was something like, "What is the use of an infant?"
Some people will recognize that we've long had zip guns and other improvised firearms that are probably cheaper and easier to acquire from nothing than a 3D printed one. Others will only see additive manufacturing as useful in quick prototyping or for production where its attributes are favorable to CNC machining or MIM.
3D printing is probably neither a relevant tool for wholesale production of contraband nor a manufacturing technique that will replace forging, investment casting, metal or polymer injection molding or CNC machining. As it matures, it will almost certainly supplement the means to those ends and maybe even replace them to a degree.
Where 3D printing of firearms is really disruptive is in the regulation of the distribution of firearms. People realize that if we are at the threshold of firearms distribution through the means of mere telecommunication, then the regulation of all other means of firearms distribution stands to become irrelevant unless the distribution via telecommunication is also regulated or prohibited. The whole system is at risk. The "approved" manufacturers like Glock, Sig, S&W, Ruger will be swept into more of a free market unless regulations are added. Lipseys and Talo will have to adjust as much as the record labels did when they were still counting album sales. FFL shops will be as relevant as Blockbuster Video. And how in the world will the tax get paid? Don't you think some people thought that maybe music and video distribution via the Internet should be prohibited to protect copyright holders? Or that we needed some way to regulate it, tax it, control it? That they needed to have the power to pick winners like Apple and Google and losers like Mega Upload, Napster and My Space?
Make no mistake, some firearm parts will probably be 3D printed as the technology matures, but what really counts here is the distribution of firearms via telecommunications, regardless of the actual processes used to realize them for the end user. It's a catastrophic change that's nothing short of what happened already to the music and movie industries. But in a similar way, it won't necessarily mean that Nashville and Hollywood will go away. But they sure can't expect to stay the same.
