RE: Big drop from 50 to 100 Yards...
That seems like an unusual large drop for the projectile. Normally if you sight in 2" high at 50 yards it should put you in or very close to the bulls-eye at 100 yards. For instance, I sight in at a 3" bull at 50 yards, wanting my group at the very top of the bull. At 100 yards normally the group will hit in the bottom 3rd of the bull. This way I know I am on at all distances...
I would try the same thing on a day when the humidity was not so bad and see what the results are. Also I have one rifle that shoots the 240 grain Cheap Shots and XTP's real well out to 75 yards. After that for some unknown reason the group breaks up real bad and accuracy is not in correlation to the earlier grouping. I switched projectiles to a 375 grain Buffalo Bullet SSB and then the group held fine out to 100 yards and better. It just must have been something the rifle did not like about the bullet.
Good luck with your rifle.