Ballistics calculators are fine. I use them and enjoy comparing predicted to actual. Most of the time the predicted is reasonably close to actual. But if I plan to shoot at game out to 175 or 200 yards I would never do so without a load that I've proven at that distance on the range.

Some bullets do funny things once they pass a certain distance. The best example I can give is the Lee REAL bullet. I have two guns that will shoot the .50 caliber 250 grain REAL into one hole groups at 50 yards. But I'm lucky to keep the 100 yard groups under six inches.