The issue is, it's a lot easier to do that directly with the gun than with the printer. Making a reprap requires some fairly accurate stepper motors, access to a RL friend with one to print out bits for you, and a pretty decent, and fairly specific shopping list from the hardware store. A simple firearm basically requires some pipe and a nail. I'm fairly technically grounded, but I opted to get a pre-made 3d printer myself for the same reason that I didn't make my own AR...it's bloody time consuming to do them right. Now, I've explored the overlap of these fields...and it IS interesting, but it's interesting in the same way as replicating a calculator in minecraft.