a Gründig Double Rifle for an unknown 12,3x63R blackpowder round, based on the 11,2x60R mauser case.
I see it on gunboards and because all the many different wildcats on mauser brass are interesting for me I contact podewils, the owner,about it. thats what he was telling me about the rifle:I bought my Gruendig D/R over twenty-five years ago whilst I was still living in Australia. The man I purchased it from was a German immigrant who came to Australia in the 1950s, from Hamburg, however he had bought the rifle in Australia & he didn't seem to know how it had gotten there. His interest was more in the single-shot stalking rifles & he sold the Gruendig to me to help finance the purchase of a rifle he said had belonged to Herman Goerring (the Luftwaffe guy). My rifle weighs a little less than 6.5lbs (about 3kg), & most people think it is a .410g shotgun at first glance!

the cartridge with a 45/70 for comparison

will send podewils the link maybe he come in and will say more about this. its a teutonic double rifle like it have to be!