May be interesting for comparing the proofstamps:

http://www.feine-jagdwaffen.de/Waffengalerie/Archiv/Doppelbuechsen

Search for: Kaletzky (wrong written, but the rifle is true)

By the way, a very fine O/U combination example is here:

https://www.progun.de/de/shop/langwaffen...1&o=preis_d


Cheers,
Gunwolf