Courtesy of "TSJ". What rifle is it? Looks like an underlever with hammers (?)and some real big barrels?

I'd guess a double 8-bore because that was the standard DGR of the black-powder period. It was light enough that you could swing it easily (assuming your gun bearer carried it all day!) but was a true stopping rifle whereas the 10-bore was sort of like a medium bore. The 10 could kill heavy game but if things went south it didn't strike a heavy enough blow. I have seen a double 6-bore in H&H's old basement and it's barrels were shorter to save weight. Hence my guess at an 8.

I agree that it looks like an 8 bore.