My gosh, this forum gives me a chance to re-visit so many guns that I had in my youth. And yes, I owned one of those monsters. It was imported by Hy Hunter and made in Germany. It was the spitting image of yours. 79 caliber smooth bored, with the end of the barrel funnelled slightly to an even larger diameter - maybe to aid in loading? All I had to shoot in it was a ridiculously patched .715 round ball. Or, for that matter, anything that I could fit down the bore. I used 3f powder for both the prime and the main charge - about 40 grains or so.
They are a well-made pistol; however the ramrod was really undersized in my opinion.
I bought mine in the mid 1960s and paid about $20.00 for it. And, when compared to those made-in-Japan flinter pistols available at the same time (they still show up now and then) it was a fine pistol, well-made and sturdy and pretty nicely finished inside and out. And, like so many others, I wish that I would have been able to have kept it.
Thanks for posting it. It's a beauty.