Earlier this week some parts of the Net lit up as a result of a discussion thread (which is just now beginning to make its rounds outside of the 3d_printing community. A gunsmith going by the handle Haveblue is said to have run off a .22 calibre pistol on a home 3D printer and fired a couple of magazines worth of ammunition with it for testing. The media's already saying that 3d printing is now firmly in the realm of criminal activity, which is no surprise because that kind of headline is guaranteed to get eyes on articles.
Here's the thing: Criminals don't do things they high tech way because they can. They do them the easy way because they don't care how they do things. Picking locks takes time; breaking a window takes seconds and a rock from the garden. Printing and assembling firearms isn't easy; it's easier to buy a gun from your friendly neighborhood hookup.
So, what's really going on here? In short, FUD. Let's break it down:
Late last year, two 3d printing hackers posted a couple of meshes to Thingiverse that caused a significant amount of controversy. First, a user going by the handle Crank posted a mesh that can be used to print a five round magazine for an AR-15 rifle. The magazine, when printed and assembled with an appropriate spring to push the rounds up (which isn't included with the mesh but can be built with a little experimentation, it is said) can be successfully used with an AR-15 rifle. A couple of days after that Haveblue posted a mesh for a reinforced lower for an AR-15 that, it is said (and I'm going to wave my "I don't know much about guns" flag high) might be sufficiently tough enough to handle fully automatic fire. Maybe.
Now, more recently, Haveblue worked up a mesh for an upper for a .22 calibre AR-15. Along with a lower and some matching miscellaneous parts (like springs, nuts, pins, and a third party conversion kit, none of which were printed on his Stratasys) and a significant amount of gunsmithing sidework (like tapping and grinding), he was able to build a servicable AR-15 chambered for .22 ammunition. In total he was able to fire about 100 rounds through it without any visible signs of wear, tear, or damage. Not bad for a fairly complex mechanism fabricated on a 3d printer.
Now, let's recap: Haveblue printed some significant parts for his AR-15 on a 3D printer. True. He also used a nontrivial amount of parts that he did not make with his 3d printer. He bought them on the open market because he's a gunsmith, with the requisite knowledge that goes into safely taking apart and rebuilding guns. He didn't make the .22 calibre conversion kit. He had to machine stuff in some intermediate steps, and it looks like he was drawing from his personal collection of parts to fill in other bits. These aren't the kinds of parts that you're going to be able to manufacture on your RepRap anytime soon because they're made of metal, and so far as I know they need to be made of metal to work. These aren't the kind of thing anyone who's not a gunsmith is likely to have knocking around in their basement workshop; they're not the sorts of parts you're like to find at your friendly neighborhood hackerspace, either. However, due to how the Gun Control Act of 1968 defines firearms (I mention this because it doesn't sound logical at all) it's actually the receiver that makes up what we think of as a firearm, so going by the letter of US law Haveblue manufactured a firearm on his 3D printer, which is where most of the FUD seems to be coming from (that, and the other gun components that have wound up on Thingiverse, which are thrown in to look extra scary).
To sum up, don't expect people to start buying Makerbots to start cranking out automatic weapons. Too much specialized knowledge and too many metal bits unique to guns are required for it to be a feasible endeavour, plus the knowledge required to make full use of a 3D printer can't be acquired overnight. You have more to fear from mass produced guns bought on the black market. Don't get sucked in by bad journalism done by people who should bloody well know better.