Calculating Holdovers and Holdundersby Linden B. (Lindy) Sisk
Revised January 3, 2008
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 400 yard zero.
Here's sample MOA dope to use.
Ok, we're going to use a 400 yard zero, so first we crank 8.0 MOA on the scope.
To calculate the mil holdunder for 100 yards, we take our dope for 100 yards, and subtract from it the dope for the range we have dialed on the rifle. Then we convert the MOA difference to mils by dividing it by 3.438.
Note: If we get a negative number when we do that, it's a hold under. If we get a postive number, it's a hold over.
0 - 8.0 = -8.0
-8.0 / 3.438 = -2.33. Realistically, on a target that close, I’m going to use a holdunder of 2.4 or 2.5 mils.
To calculate the holdunder for 200 yards:
2.0 - 8.0 / 3.438 = -1.74. I would probably round that to a holdunder of 1.75 mils.
Then calculate the hold under for 300 yards:
5-8/3.438 = -0.9. I’d probably hold one mil under.
For 400 yards, which is our zero range, we are holding dead on.
For 500 yards, we have:
12-8/3.438 = 1.16, which I would round up to 1.2, or perhaps 1.25, which might be easier to hold.
And notice we got a sign reversal. The MOA difference from subtracting our dope for the zero range from the shooting range is now a positive number, which means that we are holding over rather than under.
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 400 yard zero on my 6.5-20X50M1 Leupold.
So, with a 400 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 700 yards yourself, to ensure that you understand the process.
If you are shooting a scope with a MOA-based reticle which adjusts in MOA, or, if you are shooting a scope with a mil-based reticle which adjusts in 0.1 or 0.2 mil-radian increments, you don't have to do conversions between MOA and milliradians. Just subtract the difference between the dope for the range you are shooting and the dope for the zero range.
You can do this process with a zero range at any reasonable distance. I find 400 yards works well, because it keeps targets at most reasonable ranges closer to the center of the field of view. But you could also do it with a 1000 yard zero on a scope used for ultra-long-distance shooting which wouldn’t dial to the range you want to shoot at.
And please do remember that when using these, it works much better if you hold in the correct direction.
Really. Trust me on this.
However, consider this as an option. You are most likely to want to use holdovers and holdunders at relatively short ranges.
Consider the typical dope chart for a .308 above. Using a 100 yard zero, you can use that zero on a scope with 5 mils of marks below the main crosshairs to shoot out to 600 yards, without touching the elevation dial, using only holdovers.
To calculate those holdovers, just divide your MOA data by 3.438 to convert it to mils. Using the typical chart above, that will give you the following holdovers, rounded to the nearest 10th of a milliradian:
Memorize those numbers, or whatever applies where you mostly shoot, and you'll be able to hit targets out to 600 yards without touching your scope. Nor will you have to remember which way to hold, because it's all holdovers, just like using a Horus reticle. And that is the essence of efficient fighting with a precision rifle.
This file is: http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Holdovers/
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