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I had a play with the Strelok app and it does exactly what you are trying to do!
You can set the altitude, temp and pressure for when you zeroed the rifle, and do the same for where you are shooting...

Run it with the zero at 25 or 50m for each altitude/temp combo and compare the predicted drop at 200 maybe? Difference in drop should be close to change in impact. Using a 25m zero should put it...