I am a really big proponent of 3D printing and believe it will bring about as much change to our society as the computer did when it first started showing up in our homes; but the idea of printing out a gun that actually fires is pretty scary.
I'm not sure it this is a case of art imitating life or the other way around since the idea of a 3D printed gun has already made its way into a recent episode of CSI: Crime Scene Investigation, but in that case it was only a 3D printed handgun which could only fire one round before becoming useless.
However, in real life the team at The Wiki Weapons Project have successfully printed out an AR-15 assault rifle, the only problem is that it falls apart after firing six shots.
The project is trying to develop a fully working blueprint for the AR-15 that they want to make freely available as a downloadable design file that can be loaded up into a 3D printer. One can definitely argue the questionable legal issues around this idea but for now we can rest peacefully because at this point the team members of the project have only been able to print out the lower receiver; which is the trigger and handgrip, with the rest of the gun being made up of off-the-shelf spare parts.
As to what is causing the gun to fall apart after only six shots, the team believes it is because of the gun recoil; which causes the o-ring in the connecting section of the receiver to stock to snap.
Here is the video courtesy of The Wiki Weapons Project: