Open Sight Adjustment & Formula

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By Pierre van der Walt

 

To adjust sights follow the procedure explained below.

 

Step 1 Determine the Correct Group Center and Deviation
In the article Determining the Correct Group Center we have used an example where the statistically correct center of a 5-shot group fired at 50 yards was determined. In that example the center of the group was 0.863” (21,9mm) to the left of the aiming point and 1.5934” (40,5mm) too high. This means the group center has to move right and down.
Step 2 Measure the Distance Between Sights
The next step is to measure the distances between the face of the rear blade and the face of the front .  Let’s make it 8.976” (228mm) for our purposes. The distance between the front and the target is important as well.  For this example we take it as 50 yards (1,800” or 45 720mm).
Step 3 Apply the
The formula to adjust (drift) the rear sight for corrections is:
M = (R x E) ÷ D M is the rear sight movement (unknown)
R is the sight radius: 8.976” (228mm)
E is desired change of impact point: 0.863” (21,9mm)
D the distance between front sight and target: 1,800” (45 720mm)
Example: Imperial Metric
M = (R x E) ÷ D M = (R x E) ÷ D
M = (8.976” x 0.863”) ÷ 1,800” M = (228mm x 21,9mm) ÷ 91 440mm
M = 0.004303” M = 0.109213mm
Step 4 Apply the Calculation
The rear sight has to be moved 0.004303” (0.109213mm) in the same direction than the center of the fired group has to move to coincide with the initial point of aim. In our example that is to the right.

 

The very same method can be used to determine how much the rear sight has to be lowered to achieve the correct lowering of the point of impact.