There are a couple common methods used, with varying accuracy.
- Rifleman's Rule. Seems more common, but it not very accurate. Shooter gets MOA values from their 0-inclination range card for the horizontal distance range.
- Improved Rifleman's Rule. What Dog Rocket explained. This method is surprisingly accurate, and imo is easier to do. Shooter multiplies the drop MOA values from their 0-inclination range card by the cosine(shooting angle).
-For both cases, use the wind values for the line-of-sight range with no correction factor
-If you want to convert your hold MOA to inches of drop, you have to use the horizontal distance to do so.
I went through this whole analysis last week as I became curious after some discussion in another thread. I was not surprised at how inaccurate the standard Rifleman's Rule is. I was surprised by how good of a job the Improved Rifleman's Rule did! Plenty accurate for most hunting situations! That said, it's not much more work to type a couple numbers into your cell phone's ballistic calculator.
Plots display the vertical difference for each method relative to the 'actual' ballistic solution as reported by JBM web calculator. Aka, how much you would miss by!
7mmRM was used for this calculation.
Standard Rifleman's Rule is good to 500 yards, or longer if the inclination angle is less than 10 degrees.
Improved Rifleman's Rule is surprisingly accurate for all but the largest inclination angles. FYI, this rule works better with a short zero distance.
And, if you apply no correction for shooting angle at all....