If you are hunting Elk under 100 yards, that .30-30 will do fine, with a 170 grain bullet. If you think you will be shooting out to 200 yards, use the .30-06, and a 180 grain jacketed softpoint. Lots of factory ammo available. Find one that shoots well in your gun.
If you are going to use Muzzle loader, try to stick to something in .50 caliber for short yardage, and .54 for longer. Neither caliber is going to be a 200 yds shooter, with open sights, so practice using a tree, or walking stick as a brace to lean the gun on to shoot, and get in lots of practice at the longest range you expect to have to take a shot. Using a ML rifle is about Hunting, and not shooting. Both the .50, and .54 can kill at well past those distances, but your ability as a rifleman, using open sights, is what limits the effective range of both.