Most of the 3D printed gun stories around the net are plastic things that are lucky to get a round off. One of those is a one shot wonder by Defense Distributed, and there is a rifle floating around called the Grizzly 2.0 that has fired several .22 caliber long rifle bullets, but none of them is something you'd go to war with. Now there is a gun you can take to battle, but it's not made on a cheap 3D printer out of plastic, but a commercial 3D printer using stainless steel sintered metal.
Solid Concepts 1911
It's built by Solid Concepts, and is a classic 1911 design. It's had 50 rounds through it so far, and the company says it's still in perfect shape, ready for more. They said they chose the design because it was in the public domain, but I think it was because it was a relatively simple gun which is quite robust. Even the barrel is printed (!) making 3D printing a new possible paradigm in gun manufacture. They say they can make parts much more accurate than machining, and much less porosity than investment cast parts. (This does suggest that there is much more porosity than machined steel...). Needless to say, Police departments and cities that are freaking out about 3D guns may really have something to worry about. However, printing a decent 3D gun is never going to be cheap, and doubtful that it will be in your basement anytime soon.
Nevertheless, Philadelphia isn't taking any chances. They have just banned 3D printed guns from the city.