I am guessing that you have a load all worked out for the rifle. So getting a group with the rifle is not the problem. I would take the rifle and shoot the first group at 25 yards just to get it on paper. At this range minimum adjustment is needed. Just get a tight group with in three inches of the bullseye. Then move back the the distance you will want the rifle sighted in, be that 100 yards or what, and try and see what group it shoots. If the group is tight, move the scope. If the group is not tight, then you might have to work on your load a little before making the final scope adjustments.

Believe this or not, when I sight in a new muzzleloader with open sights, the first place I sight in at is 13 yards. I expect a very solid one hole group there. Then I move back to 25 yards. Again the group has to be very tight, and some major sight adjustment is made. After that I just start moving back to the different distances, making notes of where the group is at what distance, and I get a good chance to see how the gun holds true at strange distances.