To refer to the original question again concerning cheap, mass-produced blowback operated weapons, when would you say the first one of those actually appeared? The Sten gun? MP-40? PPSH-41? I don't think anything much earlier than about 1940 qualified as cheap and mass-produced, blowback or otherwise. Mass-produced does not also imply cheap, either.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.