billa,
Many, many years ago I owned a Remington New Army revolver, I never hunted with it (nor chrono'd it), so can't speak to the effectiveness of it in hunting. My load was 30 gr. of FFFg and it sure blew up may a milk jug and such.
And if memory serves the .45 Colt started life as a black powder cartridge shooting 30 - 40 gr. of black powder (depending on where you read it), also the .44-40 shot 40 gr. of black powder, the .30-30 30grs. All killed many a 4 legged, as well as 2 legged critter.
I'd guess that 60 gr. of BP should do it. The .454 round ball is lighter and less aerodynamic than a conical type slug, so I'd keep the distances short and maybe do some penetration tests too.