How to Calculate Windage

••• Men crossbow shooting image by Igor Zhorov from Fotolia.com

The terms "windage" and "elevation" are shooters' lingo. They refer to the lateral adjustments (windage) and vertical adjustments (elevation) to rifle sights that move the point of bullet impact until it corresponds to what you see when you align your eye with the sights. Windage adjustments move the point of impact from side to side. Windage is calculated by comparing the sight alignment, the point of impact, data on the round and the available increments of adjustment on the rifle sight.

Fire a three-round group at the center of the target from 100 yards away. Using the rests, one under the forearm grip of the rifle and one under the stock, and aligning the sights on the center-spot, fire three carefully aimed shots. Do not adjust the point of aim of the second and third shots if the rounds miss the center. You are confirming where the rifle shoots in relation to the sight alignment, not competing. If no rounds hit, bore sight the gun, or move the target range in until you are on paper.

Connect the three bullet holes by drawing a line between them with the pen. This will prevent you confusing this three-round group with a later one. If the group is not less than 4 inches at 100 yards, fire again until you have a tight group. Without a tight group, you haven't adequately eliminated human inconsistency in the shots.

Once you have a valid three-round group, calculate the lateral distance from the center of the shot-group to the vertical centerline through the center-spot. Do not calculate the distance from the group to the center point, but to the vertical center-line level with the group.

Refer to your owner's manual for the sight. It will give you increments of windage change per click or line, depending on the style of sight you are using. For example, if you are using an open iron sight, the windage adjustment is probably on the side of the rear sight, where you can turn a small screw that makes lateral movements in the sight. The manual will tell you how far each click in that adjustment screw will move the impact of the round. This will be expressed in minutes of angle (MOA). One minute of angle is 1 inch at 100 yards. If your manual says that each click equals ½ minute of angle (MOA), then each click moves the impact of the round ½ inch at 100 yards. The sight will generally have two arrows stamped R and L to tell the shooter which direction to turn the windage screw (or knob) to move the round right or left. The reason your shot groups must be less than 4 inches is that most standard ammunition has up to four MOA variability.

Apply the calculations to adjustment in the rifle, and fire another valid three-round group. Repeat this process until the impact corresponds exactly to the sight-picture you see when you have correct sight alignment.


  • Basic windage calculations and adjustments are adequate at 100 yards only if you plan to shoot at 100 yards. For longer distances, you will need a longer (and well-supervised) range, and you will need to record data at progressively greater distances, e.g., 200 yards, 300 yards, 400 yards, etc. You may find discrepancies in the claims of the owner's manual and the performance of the gun sight. Recording data allows you to calculate windage and elevation based directly on performance, and thereby refines the calculations.


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  • Men crossbow shooting image by Igor Zhorov from Fotolia.com