NPR had a report on this I heard as I drove to work. (Yeah I listen to NPR, I have my BS filter tuned pretty high to catch their liberal slant.)
The NPR article did make the point that it is legal to make your own firearm. They left out the bit that you can't make them to sell to others without a license.
NPR said that the law requiring metal in plastic guns expires Dec. 10th, and because Congress is so divided did not think it would be renewed in time.
The ATF said that they did not expect gangs and regular criminals to use 3D printing due to the cost of the printer. They pointed out that lower quality plastic makes the gun more dangerous to the user, but higher quality plastic makes it "more dangerous to others". Clearly pointing out how evil these things are.
The ATF is more worried about terrorists, so clearly only terrorists will make them, right?
They did play an interview from a documentary where the guy who made a 3D plastic gun earlier this year. He made the plans available online. He said it is about more than the 2nd amendment, it is about people around the world who live in dangerous places or under repressive governments.
Here's the link to the CNN story.
http://www.foxnews.com/politics/2013/11/14/threat-plastic-guns-grows-as-undetectable-firearm-law-set-to-expire/There was no mention of how easy it is to make a gun out of high pressure pipe. Lots of people show off their homemade handguns, rifles, and shotguns. Most of them are one shot, but that's all it takes if you know how to aim and the weapon is accurate, or you are close enough.
Even if there is no commercial ammo, it is easy enough to make black powder (yes it is dangerous), and use rocks in a pipe. I mean Captain Kirk did it to beat the gorn captain, and he use bamboo instead of a pipe.