Gun Control Is Tax-Subsidized Marketing for Illegal Submachine Guns
Because they're so easy to produce, submachine guns also became a natural go-to for non-political manufacture in countries that have strict gun control regimes. Brazil seems to be an especially fertile source for homemade automatic weapons. There's an online cottage industry in tracking Brazilian police announcements of gun confiscations and posting photos of the creative copies of commercially produced weapons—as well as weirdly innovative original designs.
This is a fine place for this quote from The Weapon:
I acquired a black-market
weapon.(Sales are all registered, but for a small premium of 50%, one
may buy a new pistol not far from the spaceport. They come in by the
shipload, as they do anywhere the local rulers utter magic incantations
to keep them out. Never let your religious beliefs get in the way of
the law of supply and demand.)
And that's not counting the 'You can make this with home workshop tools' factor.