Just to add to the discussion.. No, the Tommy gun was not solely the invention of Hollywood. It could at one time be bought from the Sears Catalog by mail order. I don't think everybody ordered one when he got his Christmas Ham and silk stockings for the missus, but...
I'm certain not everybody carried one, but they were definitely in use, along with a lot of the other weapons mentioned. Some of the better armed cops had Tommys and BARs, too. I think the practice of having to buy one's own weapon probably varied from state to state.
-Doc