This illustrates an argument I’ve made in the past to gun grabbers. Firearms technology has been around a long time. A crude, but effective gun can be manufactured from materials readily available at any hardware store, as well as other, more deadly weapons.
This book describes how to make a 9mm submachine gun entirely out of parts you can buy in a hardware store. The book includes drawings and specifications:
Luty, P. A., Expedient Homemade Firearms: The 9mm Submachine Gun, Boulder, CO, Paladin Press, 1998.
The result will definitely be better than the zip gun the guy in the article made. It's been tested.
Here are some made in a US prison about 50 years ago.