How Army Snipers Zero their Rifles

How Army Snipers Zero their Rifles

From the Kentucky and Pennsylvanian riflemen of the Revolutionary War to Navy SEAL Chris Kyle, the reputation of the American marksman has been solidified in the eyes of the public as one of a silent, deadly warrior with unmatched accuracy on the battlefield.

Today, the United States Army has made its sniper manual FM 23-10 available to the public, and many of the sniper concepts taught in it can be applied in the civilian world, especially in hunting.

The Army’s weapon of choice is the M24 SWS. Derived from the civilian Remington 700, this 7.62x51mm rifle has an effective range of 800m and can hit targets up to 1,000m away. Unlike civilian marksmen, the Army measures units of distance in meters due to the formulas used to calculate for size and range.

While the 10-40x50mm scope from Firefield may not be the same scope as the US Army’s M3A, it shares enough of its features that many of the techniques snipers use for zeroing and range finding can apply to any civilian rifleman using it.

While the military M3A has a fixed magnification of 10x, the Firefield 10-40x50mm is a second focal plane mil-dot reticle with a maximum magnification of 40. Any measurements done with the reticle will only be true at maximum magnification.

While some may think it’s odd that the Firefield 10-40x50mm has a mil-dot reticle and turret measurements in MOA, they should also know that the M3A has the same setup.

This is because with an MOA reticle, it becomes easy to measure ranges and the height of your target.

size calculation equation for snipers

MOA can also be converted to mils and vice versa.

mil-dot to MOA conversion equation for sniping

M3A vs Firefield reticle

Compare the zoom level between the two MOA reticles. Measurements for the Firefield reticle will only be true at maximum magnification.


According to Army procedure, zeroing the scope for long distance should be done with bull’s eye-style 200m targets. The Army’s procedure for zeroing the M3A scope differs very slightly from the Firefield 10-40x50mm because of the Firefield’s different turret adjustments, which are 1/4th MOA per click.

  1. Assume prone supported position 100m from the target.
  2. Line up the 1 on the elevation dial with the elevation index dot, and the 0 on the windage dial with the windage index dot.
  3. Fire three rounds at the center of the target, keeping the same point of aim each time. Do not readjust between shots. Determine the average placement of your rounds.
  4. After the strike of the rounds has been noted, turn the elevation and windage dials to make the needed adjustments to the scope.
    1. Each click on the elevation dial equals 1/4th MOA.
    2. 1 MOA at 100m = 1.145 inches or about 1 inch
  5. Repeat steps 3 and 4 until a 3-round shot group is centered on the target.
  6. Once the shot group is centered, loosen the hex head screws on the elevation and windage dials. Turn the elevation dial to the index dot marked 1 (if needed) and turn the windage dial to the windage index dot marked 0 (if needed), taking care not to readjust the scope. Then, tighten the hex screws.

After zeroing at 100m and calibrating the dial, confirm the zero by firing at targets at 100-meter increments through 900m.

200m bullseye reticle


Sniper teams use range estimation methods to determine distance between their position and the target.

  1. 100m unit-of-measure method. Visualize a distance of 100m on the ground. For ranges up to 500m, determine the number of 100m increments to the halfway point, then double it to find the range to the object.
  2. Appearance of object method. This method is a means of determining range by the size and other characteristic details of the object. To use the appearance-of-object method with any degree of accuracy, the sniper team must be familiar with the characteristic details of the objects as they appear at various ranges.
  3. Bracketing Method. Using this method, the sniper team assumes that the target is no more than X meters but no less than Y meters away. An average of X and Y will be the estimate of the distance to the target.
  4. Mil-Relation Formula. This method uses the mil-scale in the reticle. The shooter must know the target size in inches or meters. To convert inches to meters, multiply the number of inches by .0254. Once the target size is known, the shooter then compares the target size to the mill scale reticle and uses the following formula:

Equation to find range in sniping

For example, if a coyote is 20 inches tall at the shoulders and is 2 mils high when viewed through the reticle at maximum magnification:

Snipers often use a combination of the abovementioned methods, since in a real-world environment, each individual method has its own limitations. Terrain with too much dead space limits the accuracy of the 100m method and poor visibility limits the use of the appearance-of-object method.

Using these techniques, a hunter who’s already a good shot can become great. The art of long-range shooting eschews the rapid, reflexive fire of the infantryman and values patience, intelligence and precision above all else.

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