by Bob Londrigan, First Published in Front Sight Magazine, July and September 2018
Which sights you use on your pistol is very important as they can impact your scores more than any other part on your gun. At some point, there is a good chance you are going to want to change your sights -- be it the front, rear, or both sights. It may be a broken blade, or maybe you cannot adjust your sights so that Point-of-Impact (POI) aligns with Point-of-Aim (POA), or maybe you just want a different sight picture. In any case, you will need to know how to choose the best setup, what will fit your gun, and how to install it.
Let’s cover the easiest scenario first. That would be the situation where you are just replacing something that is broken and you want exactly the same setup. You just need to order the same parts to replace what is broken. If your gun is sighted in and hitting where you want it to, make sure you get the same height front and rear sight. Make sure you also get the same width front sight and the same width rear notch (unless you decide to try something different.) It can be confusing when trying to order the same sights that you have on your gun now because there are several different dovetails and sight setups that are similar. For the front sight, the vast majority of what you will see installed on competition pistols is a dovetail setup in one of two configurations:
Kimber/Novak cut – 0.330 wide x 0.075 deep x 65 degree cut, 0.320 from the center of the dovetail to the end of the slide.
STI/Heinie cut – 0.300 wide x 0.060 deep x 60 degrees, 0.250 from center of the dovetail to the end of the slide.
Custom guns may have either cut so you must contact the builder or measure closely to be sure. STI guns have the Heinie cut but if it is an STI slide on a custom build you cannot depend on it to be a Heinie cut. The two cuts are close but if you measure with a caliper there is enough difference to be sure which one you have. Don’t worry about the 60-degree cut versus the 65-degree cut as you won’t be able to tell the difference. The five degrees do not make much difference when installing the sight. I have seen some examples of custom installs that have slightly different dimensions (i.e., different distance from the center of the dovetail to the end of the slide, 0.070 deep instead of 0.075, etc.) If this is the case on your gun, you may have to go back to the builder for replacement or figure out how to modify a sight to fit.
For the rear sight there are three cuts that are most common: Novak, Bomar, and LPA. It is pretty easy to tell these apart as long as you know what to look for:
Novak- Usually used for fixed sights or combat/carry type sights. It is a 0.495 wide dovetail.
Bomar – This is a 0.359 wide dovetail with the sight elevation screw tapped into the slide.
LPA – This is a 0.359 wide dovetail with the sight elevation screw tapped into the dovetail of the sight itself.
If your sights were installed correctly the first time the dovetail should be cut to the minimum spec for the sight. Most sights as they come from the manufacturer are slightly oversize to allow for some variation in the original dovetail cut. If the replacement sight just slides in with no resistance you will probably have problems later with it falling out. Do not rely on Loctite to solve the problem of a loose sight. You want the sight to fit tightly in the dovetail. If the sight is way undersize you probably have the wrong dovetail, check this first. If it is the wrong dovetail it won’t just be loose rather it won’t even touch the sides and will be pretty obvious. If it is just slightly loose and it is the correct front sight, you have several options: order from a different manufacturer whose sights may be a little more oversize, pin the sight in place, or peen the sight dovetail and use red Loctite. Options 1 and 2 work the best.
Installing the rear sight is usually easier. Most rear sights use some type of set screw to keep them tight. You still don’t want the dovetail fit to be sloppy but it does not have to be near as tight. A slightly loose rear sight held in place by set screws and Loctite will usually hold just fine. Use red Loctite for the dovetail and blue Loctite for the set screws. The set screws are too small to use red Loctite. They will strip out if you ever try to get them loose.
A second reason for changing sights is that you are not happy with your sight picture. In this case it is a little more complicated because you have to figure out what types of sights you have now and then you will have to figure out what setup you want to try. The dovetails need to be the same but the sight blades can be different – different width front sight, different size fiber in the sight, or different width rear sight notch. Every person is a little different and you will need to evaluate your shooting, your gun, and even your eyesight in order to pick the best setup for you. Recommendations from others can point you in a general direction but you will have the best results if you analyze everything yourself and pick the best setup based on feedback from your shooting and suited to your eyesight.
First thing you will have to decide is what combination of front sight width and rear sight notch width you want. Most people will want a combination that leaves some light on both sides of the front sight. A good starting point is 50-75% of the rear sight notch filled with the front sight blade. I personally prefer more towards the 75% end. How large the front sight appears when viewed through the rear sight notch is a function of where you hold the gun (how long your arms are) and the sight radius of your gun. It is a function of the angle subtended by the notch when viewed from your eye. Using some average numbers (and some trigonometry) let us do some calculations. Assume your rear sight notch is 0.115 inch wide, is 18 inches from your eyes, and your sight radius is 6.5 inches. To fill the sight notch 50% you would need a front sight width of 0.078 inch. To fill it 75% would be 0.117 inch.
Common sights are available in 0.090 wide and 0.100 wide – either of which would be close enough to give you a good sight picture with a little less than 25% light on each side. Get too much light on each side and it becomes harder to center the sight (takes longer), get too little light on each side and if the front sight is misaligned it can be hard to tell how much it needs to be moved to be centered (also takes longer.) Another thing to consider is the 0.115 rear notch is going to appear to be roughly 6 inches wide at 25 yards. This is the width of the A zone. A good trig calculator is located at http://www.carbidedepot.com/formulas-trigright.asp if you want to make calculations for yourself with different combinations. Just remember that you are calculating the angle covered by the sight which is actually two right angle triangles combined so you have to figure out the values for one side (half the triangle) and then double the resultant value.
You must also take into account how you are going to sight in your gun when trying to decide on what sizes to get. Will you use the top of the front blade aligned with the top of the rear notch? Some will use the fiber optic aligned with the top of the notch. Which method you choose is up to you and how good your eyes are.
Here are some observations on using the fiber as an aiming point: When you use the fiber as an aiming point you are in effect using a sight blade width equal to the fiber diameter. This can result in sloppy hits if your rear sight notch is too wide. The apparent width of a 0.115 inch rear sight notch at 25 yards is about the width of the A-zone. You will also be misaligned as far as elevation if you are sighted in on the top of the blade and you use the fiber as your aiming point. You will be off by the distance between the top of the blade and the center of the dot. The further the fiber is from the top of the blade and the further from your target, the worse the problem will be. You will not have problems inside of 10 yards or so but the further out you go it will gradually worsen, until it becomes a problem. If you want to use the fiber as an aiming point you will need to use a narrower notch rear and make sure the fiber is as high sin the blade as possible.
You can test some of this partially without changing your sights. At your next practice session set a target up at 25 yards. Hold your gun out as if you were shooting it and check to see how much of the target you can see inside the rear notch. Then check to see how much of the target is covered by the front sight blade and how much the fiber only actually covers. Now check to see what happens when you misalign the sights – how far off will your hits be if the front sight is to one side of the notch or the other and then do the same using just the fiber dot. Also check the same thing on the elevation using the top of the dot and the top of the blade. This will give you an idea of what your present sight setup is capable of. You can then decide if you want to go a little wider or narrower on the rear notch and the front sight and if you want the fiber higher or not. The ultimate test is to install the sights and then test the setup against the clock to see what produces the best points per second.
The sight diagrams presented with this article are done to scale and should give you an idea of what the various sight pictures look like. They all show how the sights would appear compared to a 6-inch target at 25 yards. Pick a sight picture that looks the best for your eyes as a starting point and go from there.