Folks have posted before about various sighting problems on their rifles. A problem that occurs sometimes is when the rear sight is fully elevated or depressed and the shot group is still either too high or too low from your point of aim. To fix this problem to bring your rifle to point of aim you either have to lower or raise the height of your front sight. This is not a real hard thing to do, and we who have to shoot Italian made muzzle loaders in N-SSA shoots know it all to well, but the same formula works for all fixed sighted rifles.
Lets say you've tried to sight in your rifle at 25 yards, but after making all the adjustments you can with the rear sight you're still shooting 6 inches high at that range.
You first have to measure the sight radius of your rifle in inches. This is not hard. Take a tape measure or even a yardstick and measure from the rear of the front sight blade (the part of the blade you see when aiming the rifle), not the base of the dovetail but the base of the actual blade itself, to the front of your rear sight (the part of the sight you see when aiming the rifle), and record that measurement in inches. For this example lets say the measurement is 20 inches.
The formula for determining the amount of front sight correction is this:
Amount of Error in inches ( In this case 6 inches) multiplied by the Sight Radius in inches (In this case 20 inches) divided by the Distance to the Target in inches (In this case 25 x 36 (inches in a yard) = 900 inches). OK lets do the math (with a calculator)
6 x 20 = 120 ; 120 / 900 = 0.13 inch
In this case, if you were shooting 6 inches high at 25 yards you will need a front sight that is 0.13 inches taller then the one on the rifle now.
If you were shooting 6 inches low at 25 yards you will need a front sight that is 0.13 inches lower then the one on the rifle now.
Remember, when adjusting the front sight you always move it opposite to your hit group on the target you're sighting in on for your chosen distance. Make the front sight higher to shoot lower; lower to shoot higher; move it left to shoot right; and move it right to shoot left.
This formula will work for whatever distance you wish to sight in for. I chose 25 yards in this example under the premise you were sighting in a CAS main match rifle, and I doubt you'll ever see a target on a main match beyond 25 yards. The final corrective figure will change based on your chosen sight in distance for which you wish to shoot point of aim.
For instance, if you wanted to sight in at 50 yards (50 x 36 = 1800 inches), the amount of correction would be 0.066 inches.
I always use a caliper, either dial or digital, to measure the height of the front sight. Be cautious in removing the metal from the sight. I suggest removing a little at a time and firing the rifle again before going further. Metal is easy to remove, but real hard to put back.
Hope you find this information usefull.