An examination of the Proof Marks on the barrels and Water table will indicate whether it was Nitro or Black Powder Prooved.
The book British Sporting Rifle Cartridges by Fleming should give you several commercial loads, although these will certainly be of powders no longer available. The bullet weights and velocities will be given. I'd check my copy, but it is out on loan, which reminds me it's over due for return.
I wouldn't recommend it for dangerous game. Even Moose is a tad large and I would definately hesitate using on Bear or Buffalo. Just about every other game animal in the USA could be taken by it. For Africa it's handy for soft skinned game but not the 'Big Five' Some may differ in opinion, but we Brits didn't make the much larger calibre double rifles for just the hell of it.
Harry.
