Moreover, a halfway competent machinist apprentice could make something similar from raw bar stock and a good mill. A STEN gun can be machined in a weekend from scratch with a basic high school metal shop. Or a garage with a mill and lathe.
Homemade submachine guns from Israel and BraziL:
http://gunwatch.blogspot.com/2016/03/small-shop-guns-in-israel-carlo.html
http://gunwatch.blogspot.com/2014/02/homemade-brazilian-submachine-guns.html