Did you ever wonder where the amazing weapons in the MIB movies come from? They are prototyped using 3D printing by Moddler, a custom 3D printing service based in San Francisco using an Objet Eden 550V.
The Objet device is a good choice for this application, since it's PolyJet technology permits the creation of objects including different kinds of materials. For example, a handgun could include soft grippy pads on the handle while the rest remains rigid.
Be sure to watch this video where Moddler chief John Vegher explains how it all works.