A denizen of Sniper's Hide website sent me a P.M. asking me how to make a holdover/holdunder chart.
The process is below, so those beside him unfamiliar with the process may see how it works.
 
Making a Holdover/Holdunder Chart
 
Assume that you have a scope which adjusts in MOA but has a mildot reticle, and you want to
make a chart to tell you how to shoot holdovers or holdunders from a 300 yard zero.
 
Here's sample MOA dope to use.
 
Range MOA
100 0
200 2.0
300 5.0
400 8
500 11.5
600 16
700 21
 
Ok, we're going to use a 300 yard zero, so first we crank 5.0 MOA on the scope.
 
To calculate the mil holdunder for 100 yards, we subtract the MOA elevation for our normal 
data from the MOA elevation for 300 yards, then we divide the result by 3.438 to convert it to mils. So:
5.0 - 0 = 5.0
5.0 / 3.438 = 1.45, which we round to 1.5
 
To calculate the holdunder for 200 yards,
5.0 - 2.0 / 3.438 = 0.87, which we round to 0.9
 
The calculate the hold OVER for 400 yards,
8 - 5.0 / 3.438 = 0.87, which we round to 0.9
 
Now, notice carefully that we've got a sign reversal, because now we are holding over 
rather than under.
 
As you make your chart, it's up to you to figure out how to put the data on the chart in a way that 
you'll remember to hold under at ranges shorter than your zero range, and to hold over at ranges 
longer than your zero range.
 
It seems more natural to me to make the holdunders negative in sign, and the holdovers positive. 
Use whatever works best for you. 
 
So, here's my sample chart of holdunders and holdovers for my load in my AI AE with a 300 yard 
zero on my 6.5-20X50M1 Leupold.
 
Range Holdover/Holdunder
100 -1.5
200 -0.9
300 0
400 0.9
500 1.9
600 3.2
700 4.7
 
So, with a 300 yard zero on that scope, which has 5 mils both plus and minus from the center crosshairs, 
I can shoot anything between 100 yards and 700 yards.
 
You might want to do the math for 500, 600, and 700 yards yourself, to ensure that you understand the process.
 
Of course, now I have on my rifle a U.S.O. SN-3, with centimeter clicks and a Horus H25 reticle.
 
Instead of memorizing a holdover chart, I memorized my elevation data in mils. Since I'm always holding 
over, except at ranges less than 100 yards, I no longer need a holdover chart. I'm done. Much simpler, 
and I never have to do another MOA to mil-radian conversion.
 
But, if you need to shoot holdovers and unders, above is how to calculate them. 
The process works from a zero at any range - you just have to do the calculation again for a different 
zero. If you're shooting the drill known at Rifles Only as Moving Chaos from the tower, a 400 yard 
zero works better, because that's how far it is to the mover.
 
And please do remember that when using these, it works much better if you hold in the correct direction. 
 
Really. Trust me on this.