I've done hundreds of parts via 3D printers and have been using the various technologies for the past 10 years. Not 20 feet from my desk at work sits a 8 year old stratasys FDM machine which is an ancestor of the machine I imagine was used for the model shown.
I'm skeptical that a were at the point where a 100% "printed" gun could be made safe and effective, and EXTREMELY doubtful that a gun printed on an FDM machine would be workable.
Consider this, these prototype technologies are trying to reach a point where parts created by them are as strong as a part made in similar material by conventional processes. They're not there, not even particularly close. Consider an example from Stratasys website.This is the strongest material available and where I would start if I were designing a firearm printed in an FDM (actually I'd probably start by writing a will, but putting the danger aside).
http://www.stratasys.com/materials/fdm/~/media/Main/Secure/Material%20Specs%20MS/Fortus-Material-Specs/Fortus-MS-ULTEM9085-01-13-web.ashxThis is a PEI or "Ultem" plastic for use in an FDM machine, Ultem is high end stuff and unless I've overlooked something this is the strongest stuff currently used in an FDM machine. This material is only about 1/2 as strong as a part molded or machined out of a basic grade of ultem.
Why does it matter? Because if you can't make a gun out of plastic via old-fashioned methods (as far as I know you cannot) you definitely can't make a plastic gun in a 3d printer. In terms of performance plastic is just no where near the strength needed to handle the pressure and heat associated with a firearm. The STRONGEST (and most expensive) plastic generally available is PEEK, it's used in high temperature applications and medical applications and in some cases can be used to replace metal parts. Even taking this plastic, reinforcing it with a 30% carbon fiber fill, you wind up with a material that has 1/3rd the yield strength of mild steel, probably about 1/6-1/10 the strength of a treated alloy steel such as typically used in the barrel and receiver of a firearm. Plus the plastic won't dissipate heat well, resulting a plastic gun being HOTTER on the inside than a steel one, and even PEEK (which is the king of plastics) will weaken significantly before steel's even getting worried. Even basic PEEK runs something like $15-$30 /lb in bulk, much more in small amounts. I hate to consider what a carbon fiber filled grade costs!
Now, there are 3D printing technologies that use metal (google DMLS, or direct metal laser sintering). These MIGHT could be used to make a firearm. They're really a non-issue for the near future however as the "printers" are extremely expensive and the technology far less easy to implement on a DIY basis than FDM (which is what most people in the DIY community call a 3D printer, FDM is actually only one of probably dozens of technologies). DMLS parts are still extremely expensive, anything the size of a handgun would cost thousands of dollars and I doubt DMLS machines exist that could print a rifle or even a carbine. More likely one would print all your gun parts in an FDM machine and then use those parts as patterns to investment cast metal parts, that could probably be done by anyone with some know-how and a furnace. I'd still stand very far away when they started shooting such a weapon.
