Rifle Scopes Lasr Sights, Binoculars, and Accessories

Using Mil-Dot Rifle Scopes

Understanding a MilDot Reticle

Range finding rifle scopes offer a way to estimate distance to target. They do this through passive means; that is, there's no signature, such as a laser beam at the target. The most common of range-finding reticles is the Mil Dot. This article we will describe how to use a Mil Dot Reticle for estimating range.

The Geometry of the MilDot

A MilDot Reticle consists of vertical and horizontal crosshairs with milliradian-sized dots, called mildots for short, evenly spaced across the cross hairs. To understand the significance of the dot in a Mildot Reticle, we'll have to take a quick trip back to high school geometry. The MilDot is based on the Radian. A radian is an angular measurement of a circle where the circle's radius equals the length of the arc sectioned off by the angle. So, the Arc to radius length ratio is one to one. The "milli" in a milliradian means one one-thousandth of a radian. Therefore, in a milliradian the arc length to radius length is one to one thousand.

Using the above description, we can then understand how the mil dot is used in range finding. The crosshairs each represent arcs of horizontal and vertical circles with the eye being the center of a circle. The distance to the target is then the radius of the circle and dots cover a portion of an arc of the circle. Knowing that the milliradian is 1/1000 of the radius, we can use the formula that the distance between dots of a mil dot equals one unit per thousand units; that is, one yard at a thousand yards; one meter at a thousand meters, or one inch at a thousand inches, etc.

Focal Planes

Rifle Scopes have two focal planes, called the First and Second focal planes. The Reticle of a riflescope can be located in either the first or second focal planes. When the reticle is located in the first focal plane of variable magnification rifle scopes, the mildot reticle can be used at any magnification level as the reticle will shrink or grow with the change in magnification. When the reticle is in the second focal plane of a riflescope, the reticle size is fixed regardless of the magnification level. If this is the case, the mildot is typically calibrated for the highest magnification level. If you're unsure contact the manufacturer or look at the owners manual that came with the rifle scope. You can also test the rangefinding system against a known target size to reveal the calibration.

Practice,

Using a mil dot reticle for range finding takes a lot of practice. Additionally, you must know the size of the target for comparison purposes. Try setting known-size targets at distances you think you may want to use the rifle scope and observe. Test what you see. Does it make sense? Does the rangefinding system work for you? It does? Great; now get out and practice some more.

Finally,

Understand that MilDot reticles provide a system for estimating ranges. There are a lot of variables in play; the distance, target size, your eye. If you're looking for precise rangefinding measurement, you might want to consider using a laser rangefinder.

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