RE: 1st timer with aT/C WHTE MOUNTIAN CARBINE
If it is an older WMC it may even have a faster twist barrel. A friend of mine who has one loves shooting heavy conicals in his with about an 80g charge of whatever powder you like to shoot. I would recomend good ol black 2F if you can find it if not T7 seems to work pretty good in sidelock rifles.
Good luck those are nice brush guns.