Everyday, No Days Off has a video where a guy made a working shotgun from some pipe and a staple gun. If you’re short a staple gun, you can just use a length of pipe with another piece of pipe with a slightly larger inner diameter and a nail / screw through the bottom.
Putting on my broken record hat – guns are NOT difficult items to make. What’s difficult to make are reliable weaponry that lasts a long time. If someone finally figures out how to get the toothpaste back in the tube and manages to make every last firearm disappear tonight, criminals will simply make zip guns. They’d be cheap, untraceable, and disposable. The fact that they couldn’t get hundreds of shots out of them is irrelevant.
Instead of a gun free society, what you’d have is a disarmed populace who could not fight against the criminals, who’d be armed well enough to ply their trade. But that’s logic, and totally an anathema to the anti-gun crowd.