I take it there is no maker on the rib? I have the exact same actioned gun in a 20g. Ejector that is now a 30/30 double rifle. The maker on the original rib is a H. Barella and marked Berlin & Suhl. Engraving is different than yours as well as some other small details. But the action is exactly the same. proofs too.

I always assumed it was an action supplied to the trade by Sauer or something.

B.Dudley