Thursday, March 18, 2010

Estimating Range With A Mil-Dot Reticle

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It's a common feature found on many scopes and other optics, but what exactly is a Mil-Dot reticle, and how do you use it?

It's important to make clear the distinction between Minutes of Angle and Mils. A Mil, or milliradian is equal to about 3.44 MOA. Most reticles are marked in milliradians using Mil-Dots, while adjustments through the turrets are usually made in fractions of an MOA.

Variable magnification scopes come in two types: First Focal Plane (FFP) or Second Focal Plane (SFP) reticles. Most American scopes have the reticle on the second or rear focal plane, so that the reticle stays the same size as the zoom is changed. European style scopes have the reticle on the first or front focal plane, such that as the magnification on the scope is increased the reticle increases in size. European Mil-Dot reticles are accurate for range estimation at any zoom level. For American style rear focal plane reticles on variable magnification scopes, the Mil-Dot size estimation is only accurate at a certain zoom level. For most variable scopes with a second focal plane reticle the proper magnification is 10x, though this does vary depending on the manufacturer. Consult your owner's manual to determine what zoom level your Mil-Dot reticle is designed for.

Based on a presumed chest height of 15 inches, this deer would range at approximately 1,389 yards.
The first step in using a Mil-Dot reticle is accurately measuring the size of a target in Mils. Once a target of known size is measured in Mils in the scope, a simple calculation is used to estimate range to the target and compensate for bullet drop. Accurately measuring the target in Mils is not easy, and it is necessary to get an approximation down to around one tenth of a Mil. In the photo shown to the left, the chest of the deer reads at approximately 0.3 Mils. Shown here on the internet, this measurement is fairly easy to see, but when staring down a scope that you are struggling to hold steady at a target that may not be holding still, it becomes much more difficult to get an accurate Mil read.

The formula for computing the estimated range is accomplished by taking the target size in yards, multiplying that by 1000 and then dividing the result by the target measurement in Mils. The result is the approximate distance in yards to the target. The formula for meters is the same, with the target size in meters multiplied by 1000 and divided by the target measurement in Mils giving the approximate range in meters.

So, if you have a man sized target that is six feet tall, you would compute Target size in yards (2) multiplied by 1000 and divided by the measurement in Mils. If a six foot tall target, for example, measures 3 Mils, the formula would be 2 X 1000 / 3= 667 yards.

Size of Target In Yards X 1000 / Mils read = Range to Target (in yards)

The formula is the same for meters:

Size of Target In Meters X 1000 / Mils read = Range to Target (in meters)

There are two ways to compensate for bullet drop. One is to use hold-over. This involves changing the point of aim to be somewhere other than the center of the cross hairs of a scope. The other is to adjust the turrets the appropriate number of clicks until the target can be centered in the cross hairs. Once the range is known, the shooter can then make the necessary adjustments to the elevation using the scope turrets, or hold over the proper amount using the Mil-Dots as an aiming system. If you know your rifle is zeroed at 300 yards for example, your target is an estimated 400 yards and your bullet drop at 400 yards is 15 inches, then you would hold just slightly less than 1 Mil high (1 Mil-Dot is 14.4" at 400 yards).

Click to download our free Mil-Dot Range Guide (*.PDF
There are numerous tools on the market that make range estimation using a Mil-Dot system fast and easy. Some use a slide rule type setup where the target size and measurement in Mils is input to the tool, and the range estimate is then shown. Others use a spreadsheet to allow the shooter to quickly find the range estimate. You can download your own "cheat sheet" by clicking on the image shown to the right. Simply save the *.PDF file to your computer and print it out on a plain sheet of 8.5x11 paper. Fold the paper into thirds and cut or tear carefully along the creases and you will have three copies of our Mil-Dot Range Estimation guide you can laminate or simply fold up and take with you.

Here are a few more quick references to help you quickly and easily estimate range using a Mil-Dot reticle: The average adult deer chest is around 18 inches tall. At 100 yards, that deer chest will take measure 5 Mil-Dots, 2.5 dots at 200 yards, 1.6 dots at 300 yards, and 1.25 dots at 400 yards. For calculating holdover, remember that 1 Mil is about 3.44 MOA, so 1 Mil at 100 yards is about 3.5 inches. At 200 yards, that same Mil is about 7 inches, at 300 a single Mil is 12 inches, and at 400 yards is just over 14 inches.

The only way to get good at using your Mil-Dot reticle to estimate range is to practice. Take a hike and set up multiple targets of known size (1 yard/3 foot squares of poster board on stakes work great) at various distances from your shooting bench. Head back and get out your estimation guide, calculator, or pencil and paper and find your measurements and estimated range. Confirm your estimated range figures with a laser range finder, GPS, or other device. Soon you'll be able to quickly and easily estimate the range to nearly any target.

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