Late in the reply and some of this has alredy been covered. Here is what I do.

First of all "bore sighting", if well done, will usually get you on paper at 100 yards, but I start at 25 yards. I use a "poster" and a standard 100 yard "gridded" target. I put the target in the center of the poster. I aim at the bull and fire 1 shot to see if I am anywhere on the poster. If so, which I would expect to be at 25 yards ! ... I move the scope settings until I am dang close at 25 yards.

Then I move to 100. I aim at the bull and fire three very carefully shots. I find the center of that 3-shot triangle and use the distance of the center from the bull to make the first adjustments to the scope.

I'll fire 3 shots at the bull and repeat as described above until I am satisfied that I am as dead on as my rifle/ammo combination can do.

I use a 308 Win., 165 gr. Game King loaded a littel hotter tahn about mid range of Speer's loading manual. This load just happens to group great out of my rifle. Where I hunt the longest shots are going to be 200-250 yards. I zero my hunting rifle 2" high at 100. That lets be aim dead on across the entire range that I will encounter.