Mashable created a mini-documentary about one average guy (not a technical 3D CAD genius, nor a gun expert) and his attempt to print the DefCad Liberator pistol. I think at this point you need to know a bit about guns and a bit about CAD to print a gun successfully. This guy obviously knew nothing about guns (waving the gun barrel around, calling the grip a handle). Nonetheless, it is an interesting video …
Thanks to the person who sent me this link (I lost his/her email).