Best way- zero and shoot at distance. You really need to do this anyway even if you have a properly zeroed optic, as the BDCs are really just compromises and educated guesses with generic ammo performance.
Option 2- Employ the links below to give you an accurate estimate prior to confirming at distance.
Metric ConversionBallistic Calculator
You will nver know how far off you will be with your gun, with your ammo, at your range, etc. etc. without confirming the BDC at actual known distances. If you do not have access to those distances, the calculator will give you a pretty good idea.
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