Hey buddy, I have the same scope on my 06 and 100 yds has been the best sight in range for my setup. In fact, I think that 100 yds is the average round about distance for most people.
I hope you had that scope Boresighted... If not that should be your first step.
100 yards is an ideal distance to sight in your Muzzleloader, you may want to start at 50 yards for the first few rounds to see what your rifle is doing and then if it's shooting OK at 50 yards you can move out to 100 yards for fine tuning.