Quote History Quoted:
"you have ACOG X, but you're running barrel length of Y and ammo Z, here are what the hold over points will be"
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Except on Tuesdays and alternate Fridays.
Stuff like this is calibrated to a certain rifle with a certain ammo and EVERYTHING including barometric pressure are going to change thing to some degree or another.
for example, USGI ammo, while junk, certainly isn't match grade.
You have to have realistic expectations when using something like a BDC and it often boils down to practical experience. I use the term 'some idea' of what will happen meaning in the ball park.
Something like an ACOG is nothing more or less than just another tool to work with.