Zip Guns
A good article. Yes, 3D Printers still can't print guns. Only the people who need to be shown the picture of a cartridge and told the copper part flies down the barrel ever seem to buy into this.
For some reason, printing a gun is the peak-evil use task the mind comes up with. Like an atom-printer could make TNT, an atom-assembler could make Plutonium. Yet, the current 3-D printers have absolutely no functionality needed in making a gun. The only thing plastic on most guns are the grips. "Polymer" frame guns are popular, but they are made from some seriously high pressure injection moldings as strong as steel.
However, The Big Picture -- can Joe Blow make a gun in his basement? Yes, has been able to for hundreds of years. These days it might be called a "Zip Gun", see Wikipedia. You just need a tube, some tube. You stick a cartridge in it, put a cap over the end. Hole in the cap, a nail into the hole. Big rubber band to pull back and hit the nail, fire the gun. You're done. Do anything that looks like rifling in the tube -- you're legal (in USA). Could even make them and sell them.
Ah, but a 3D printer can make a frame with grips? No, too soft. Buy a cap pistol, use it. The cost a bit less than a 3D printer.