hoppdoc
One thing I have discovered with my 75% rule is that the 2 loads have nearly the same trajectory.

Look in a Hornady manual at their 500gr bullet at 2100fps and their 350 gr bullet at 2300fps.

You will see out to 300 yards their trajectories are nearly identical, for hunting purposes.

My full weight loads in my 450/400 [400gr bullets] and in my 450 No2 [480 and 500gr bullets] travel at 2100 to 2200fps. My 75% bullets [300 gr in the 400 and 350gr in the 450 No2] travel about 2330fps.

If they hit the same place at 100 yards [and they do] then they will hit the same place [close enough for hunting] at 300 yards, and they do.

My Nitro for Black loads in my 450 No2 hit the same place as full power loads at 50 yards but since their velocity is reduced their trajectory is not the same at 100 and out.

I have found it much easier to get different bullets to hit the same place with a double than a bolt rifle.