Useful to know, KK, the caliber of your double and the weight of bullet and brand of powder you are using. Lots of parameters engaged on slower vs faster powders, (quite apart from loading density); on weight of bullet the barrels were initially regulated for (should be stamped among the proof marks) and the rule of 3/4 for trying lower bullet weights.
Another key question is how you are holding the rifle from the bench as you basically need to hold it much as you'd shoot it in the field (which is why the Brits use benches you stand at to regulate doubles).
None of it is rocket science, but do need to go through the process for best accuracy and velocity combination.
Yes, you for sure need to see how it prints at 100, but I'd guess you'll see a crossing composite group of about 5 inches...
Regards,
Tim