Estimating field target distance with a mil-dot scope

 

Assuming that the distance from the average field target base to center of the kill zone is 5.5", it is possible to use a mil-dot scope to accurately estimate range to a target as a primary means of range estimation (hunter class), or as verification of  focal distance estimates  with high powered adjustable objective riflescopes (open or piston class).

The first step in this procedure is to determine at what magnification, your mil-dot scope represents a true milliradian of measurement.  If this is not known, mark a target so that the vertical distance between two aiming points is 1.8".  Place this target at  EXACTLY 50 yards and place the crosshairs on the upper target.  Then adjust the magnification until the first dot below the crosshairs exactly covers the lower aiming point.  The magnification at which this occurs is the magnification that measures 1 milliradian between the centers of two adjacent dots on the mil-dot scope.

Once this magnification is known, the vertical element of the reticle can be used as a measuring device to determine distance to field targets.   Assuming that the average field target is designed so that the distance from the center of the kill zone to the base of the target mechanism is 5.5" the following chart can be used to accurately determine distance to the target:

 

yard mils yard mils yard mils yard mils yard mils

10

 15.2 20 7.6 30 5.1 40 3.8 50 3.0

11

 13.9 21 7.3 31 4.9 41 3.7 51 3.0
12 12.7 22 6.9 32 4.8 42 3.6 52 2.9
13 11.7 23 6.6 33 4.6 43 3.5 53 2.9
14 10.9 24 6.4 34 4.5 44 3.4 54 2.8
15 10.1 25 6.1 35 4.4 45 3.4 55 2.8
16 9.5 26 5.9 36 4.2 46 3.3 56 2.7
17 9.0 27 5.7 37 4.1 47 3.3 57 2.7
18 8.5 28 5.5 38 4.0 48 3.2 58 2.6
19 8.0 29 5.3 39 3.9 49 3.1 59 2.6

 

Since the typical mil-dot scope only provides for 10 mils of measurement on the vertical, several techniques can be used to accurately determine distance to targets under 20 yards.  The most simple method is to place the upper-most mil of the vertical reticle on the center of the kill zone and observe where the lowest mil falls on the target.  Then re-measure to the base of the target mechanism (or face) from the point where the lowest mil mark initially fell on the target.  Add these two measurements together, and refer to the above chart for distance to the target.

The second option is to reduce the magnification of your scope to half of its true milliradian measurement magnification.   This will have the effect of proportionally reducing the mil measurement by half so that a target at 10 yards would now measure 7.6 mils from center of the kill zone to the base of the target mechanism.  If this option is used, it is important to remember to return the magnification to its true milliradian level prior to determining aimpoint for purposes of shooting.

 

Example:

The following field target is placed at an unknown distance.   Knowing nothing more than the approximate distance from the center of the kill zone to the base of the target mechanism (5.5"), it is possible to determine the distance to the target:

 

Set the scope's magnification to the setting that generates a true milliradian of measurement for the scope, and place the uppermost mil mark in the center of the kill zone.

 

 

Count the number of mil-dot marks from the kill zone to the base of the target mechanism.  In this example, the distance covers approximately 8.5 mils.

Referring to the above chart, the distance that corresponds to a measure of 8.5 mils is 18 yards.

It's that simple!  This method provides a quick and accurate estimate on range for hunter class field target, and a means of verification of range finding distance with use of high magnification adjustable objective scopes.