The project must have been a local gunsmith put together without any serial production. It must have been created as an attempt to say, “Why not?”
The thing is so massive, it looks like it requires a breech block similar to a recoilless rifle or artillery cannon just to load. It includes a massive compensator, and iron sights. Why they even bothered with a compensator on a cartridge so large in something like a handgun…
https://www.thefirearmblog.com/blog/2016/02/10/50-bmg-single-shot-handgun/
Not to mention 50 BMG is typically made to be shot from ~28 inch barrels. This looks like less than 10 inch of actual barrel.
3” at best