ummm math? If one slug flies differently than another, there's no point in sighting it in, you'll never be consistent.
If you have your muzzel velocicty, you have enough to predict your arc. If you're doing the "gnats ass" of factoring in drag, you need more data but it's still not hard...you also have too much time on your hands AND your wasting it.
Stand on the great salt lake and fire a slug perfectly perpendicular to gravity. It will take just as long to hit the ground as a slug dropped from the barrel.