Fiber Optic Sights

by Bob Londrigan, published in Front Sight Magazine, March 2005

For Limited class shooters, the fiber optic sight has become the sight of preference over the last several years. Robin Taylor suggested that it might be time for an article on fiber optic sights and I agreed.  We will go over how to install the sight, how to maintain the sight, and what some doís and doníts are with regard to using fiber optic sights.

To install a fiber optic sight you follow the same procedure as you would to install any other type of sight with a dovetail. You begin by determining the size of your front dovetail cut.  Youíll need this information to see which sights will fit your gun.  The two most common dovetail dimensions currently in use are 0.330 x 0.075 x 65 degrees and 0.300 x 0.060 x60 degrees.  The first measurement refers to the length of the dovetail, tip to tip, at its widest point. The second measurement is the depth of the dovetail from the lower side of the blade to the bottom of the dovetail.  The third measurement identifies the angle of the dovetail. Other crucial measurements include the distance from the front of the slide to the center of the dovetail and the height of the blade off the slide.  The height of the blade off the slide should be kept the same unless you want to change the point of impact of the gun. For instance if your rear sight is sitting up very high and you want to lower it, then get a lower front sight.

Purchase a sight that most closely matches your measurements.  Most sights available today are actually oversized compared to the dimensions that may be listed on the package.  Thus, a sight that claims to be 0.330 wide may actually be 0.335 wide or even wider.  Manufacturers do this because front sight dovetails vary widely and you want to be sure that the sight fits tightly when you are done. If you were a gunsmith, the installation would involve measuring the dovetail on the gun using pins and then doing the same on the sight. 


Using a dovetail cutter with the matching angle, the gunsmith then cuts the sight the proper amount. The gunsmith would reduce the 0.330 measurement by the amount that had been measured while maintaining the angle of the dovetail. 

However, since most of you donít have a mill handy, you have to take a different approach.  You could take a triangular file and file the dovetail a little at a time until it fit, but it is quite difficult to maintain the 60 or 65 degree angle and stay square at the same time.  An easier method is to take material off the bottom of the dovetail. For every 0.001 inch you take off the bottom of the dovetail, you are taking approximately 0.0017 off the width of the dovetail (the exact amount depends on the angle of the dovetail). To get the normal 4-5 thousandths you need to take off the width of the dovetail you will need to take about 0.003 inch off the bottom -- about the thickness of a sheet of paper.  This is most easily accomplished with a flat file that enables you to maintain a flat, true bottom on the sight.  Take a wide file, lay it on your workbench, and then scrape the bottom of the sight across the file. 

Take material off the bottom until you are just able to insert the sight slightly into the dovetail.  Then tap the sight into place with a brass punch.  Check to make sure the bottom of the blade is not contacting the slide (especially if you have taken off a lot of material from the bottom of the dovetail.) Also make sure the punch bears against the dovetail itself and not the sight blade.  If you try to tap against the sight blade you may bend or break the blade.  A drop of red locktite in the dovetail will help to hold the sight in place.

Maintenance on your front sight consists mainly of keeping it clean and bright.  A little information about how fiber optic material works will explain why. True fiber optic rod is composed of a core layer of material that is impregnated with a fluorescing compound that reacts to light.  This fluorescing compound is surrounded by a thin sheathing layer that has a different index of refraction than the compound. Ultraviolet light enters through the exposed sides of the fiber.  The light is trapped within the fiber because the difference in refractive indexes between the core and the sheath do not allow the light to reflect back out through the sheath.  The UV light causes the material in the core to fluoresce and emit visible light out the end of the tube where there is no sheath.  The longer the tube, the more light is captured and emitted out the end. One benefit of the physics of the fiber optic is that on a cloudy day you still have lots of UV light available to light up the fiber.

As you can see, the key to the fiber optic functioning properly is the outside sheath.  This is what lets in the UV light and then traps it so that it can come out only on the ends.  Therefore, it is critical to keep this sheath intact and clean.  A dimming fiber optic means the sheath is either dirty and canít let in as much light or it has been damaged and is not longer able to trap light.  Following are some tips to help you keep your fiber optic bright:

  1. Keep the fiber as clean as possible but do not do anything that deteriorates the sheath.
  2. When you install replacement fiber, take care to keep the sheath intact as much as possible.
  3. Stay away from chemicals harmful to plastics such as brake cleaner and gun scrubber for cleaning the fiber and when cleaning your gun. 
  4. Replace the fiber every once in a while when it gets too dirty to clean, or when the sheath deteriorates. I recommend you replace the fiber before each match just like the battery in a dot sight.

Installation of replacement fiber is an easy operation:

  1. Remove the broken fiber from the sight.

  2. Insert replacement fiber from the muzzle end and leave approx. 1/16 inch sticking out (the more you leave sticking out the bigger the dot).

  3. Melt the end with a cigarette lighter.

  4. Hold the melted end tight against the sight and cut the end closest to the muzzle, leaving 1/16 overhang.

  5. Melt the muzzle end of the fiber while holding the fiber tightly against the sight.  It is important to make sure that the fiber is snug in the sight with no play back and forth. A loose fiber will break very quickly.

It may be a little more trouble to use a fiber optic sight, but most shooters will agree that the benefits significantly outweigh the extra effort.  A good, bright fiber optic sight will help you see the front sight, get you on target quicker, and speed up target acquisition.

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