120-140 grains seems a bit high. What you get with rifled guns of calibers higher than say .62, is the projectile holds a great deal of its energy upon impact at closer ranges, although it has a lower velocity than say a .50. Thus..., it cuts brush, and goes through bone better and deeper at 75 yards than would a .50. Those heavy Germanic rifles were often used by folks on horseback in secondary growth forests, or by the game keeper to finish off the dangerous game that the nobleman failed to down with a lighter rifle. Bison were hunted with 12 gauge shotguns from horseback in the 19th century, but the riders were pretty darn close at the time.
The old old rule of thumb is that one didn't use powder more than the volume of the shot, and used the same powder load when shooting a single ball (when using a smooth bore.) As the guns from .62 and up were more commonly smooth bore, when they were occasionally rifled, the rule was kept. After all, the patching will form a better seal and give you better ballistics in the rifled barrel than in the smooth bore.
SO..., weigh your round ball. Then measure out the same weight in say #8 shot. THEN set your powder measure to throw that amount of shot, and you'll have it set for a good starting point for volume in 2Fg black powder. (I'm betting it probably won't be more than 100 grains)
See how the gun shoots, how much punishment you take, how much the bullet drops over distance, and go from there. I'd also check the muzzle velocity if you have access to a chronograph. You'll probably see equivalent ballistics to a non-magnum 1oz. 12 gauge slug.
If you think you have to reach out to 100 yards..., go with a .58 for moose in roundball, or not bigger than a .62. OR...., go with a barrel that has a fast enough twist for a conical, and use a conical in say .50 - .54.
LD
ack bears, huh?
