Cape Gun is more of a British term, but this is a sxs 2 barrel affair, 16 ga left and uncertain rifle right. Stiegele-Jagd is still in business in Munich, but the family had to sell out in 1927 due to the "riotous lifestyle" of the 3rd generation, C. Stiegele Junior (from Stiegele-Jagd webpage). It's his name on the firearm. My extended family includes several Bavarian hunters, so I couldn't resist the Munich make. I will include pictures when I have it in hand.

I'm asking for "nominations" for rifle caliber possibilities, given the starting point of a chamber cast by the seller. He measured it as 11.7x51R Danish. The time frame is right, but that is a Danish military round chambered in Remington Rolling Blocks. But neither I nor the seller can find a similarly dimensioned round. It's not too far from 45-70, but it's shorter by a couple mm.

I like working with obsolete rounds and have a fair amount of experience loading blackpowder. So, what's your guess for a straight-walled (maybe some taper), 46 caliber, 2" case?