Formula For Changing Height of Front Sight

[Big John Denny]

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.

Remeber, 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.

Hope you find this information usefull.

[Joyce (AnnieLee)]

Before you start filing....

Do two things:

1) Put it down for a few days, then take it out and try again. I thought I had a revolver that was way off, but when I shot it the first time, I was tired and not well focused. It was fine when I tried it again.

2) Have someone else shoot the firearm to see if he gets the same kind of off-set groupings. You could be pulling your shots: it could be your technique and not the firearm.

Just a thought,

AnnieLee

[The Arapaho Kid]

Someone told me today that if I raise my back sight a click, or two that'll drop my round hits on the target.   I don't think so! I think the prupose of raising the back sight is to raise the round hits higher.

The propceedure that Big John mentioned is just a little too technical for me.  I think I'll just have a gunsmith install a whole new front sight.

[Jose Grande]

Big John,thanks. That is so simple,I'm left slapping my forehead,saying why didn't I think of that ?? I knew there had to be a way to figure it,but I never knew what it was. Thanks again.

[Hemlock Mike]

Several years ago, I did the same calculations for my RV because it shit low at 25 yards.  It figured that I needed to drop the front sight about 0.040".  I stopped at half that to try it out and it was dead on !!  Go slowly and try it out.  It's easier to remove metal than put it back 

Mike