I made one by taking a Thompson SMG barrel, cutting down the end of the barrel till the chamber was .45 GAP length, and then making a new barrel extension from scratch. It uses 9mm Sten mags with a KKF magwell block. I made my own Oly type pistol caliber upper receiver by ordering Olys ejector spring package and drilling out a flat top receiver I had lying around.
Runs like a raped ape. It is currently being parkerized. I will be using a LaRue free float hand guard with flip up front sight that sits on the hand guard as the barrel is too thin to machine for a .750, standard front sight base and it would add to the cost to machine it to .625, A1 diameter and then I'd have to search for A1, front sight base.
I haven't had a chance to check accuracy or velocity yet but it feeds, extracts, and ejects very well. I can get 16 rounds in a Sten mag.
Sorry the pictures are out of focus.