When I started black powder hunting back in 1979 my rifle was a .50 TC Hawkins percussion and my kit consisted of 4 glass tubes with 90 gr of black powder, a box of pre-lubed maxi balls , a tin of primers, a small bottle of solvent and a few cleaning patches. Back then all my friends told me to get a real gun. I ended up killing my first deer, an 8 point with an 80 yard shot.
I'm not a black expert but I think a .54 would be sufficient for elk not sure about moose.