Front Sight Installation

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

One of the most common modifications made to competition pistols involves switching out the sights.  You may be trying to get a different sight picture, trying to get a pistol with fixed sights to hit point of aim, or trying to replace a broken sight.  Whichever scenario applies, you’ll need to change your sights. Changing sights is a fairly easy procedure once you know what to do and if you have the proper tools. This article will help you with the “what you need to know” part, and I’ll give you a list of what tools you need to have on hand. 

First the tools list – to change out your front sight you’ll need a padded vise or some other mechanism that holds your slide securely without scratching it, calipers for making precise measurements, a file with one safe side, a brass punch, a hammer to strike the punch with, a large file or a sanding block, and some red (permanent) Locktite.  If your sight has a pin in it, you’ll also need a punch of the appropriate size to remove the pin.

Measuring the dovetail cut Once you have your tools and you know what type of sights you want to switch to, you must determine what dovetail cut your gun has. Although some factory guns have staked on sights, the norm for custom guns is sights that fit in a dovetail cut in the slide. Most custom guns will have a front dovetail cut with one of the following two dimensions:  0.300 x 60 degree x 0.060 or 0.330 x 65 degree x 0.075.  The first number in these dimensions represents the width of the dovetail, front to back on the slide (at the widest point).  The second number is the angle of the dovetail in degrees, and the third number is the depth of the dovetail. 
Measuring the dovetail cut Another measurement you want to be concerned with is the distance from the end of the slide to the center of the dovetail. This measurement for the 0.300 wide dovetail is usually 0.250 inch.  For the 0.330 wide dovetail, it is 0.320 inch although there are a few that measure 0.250 from the front of the slide. The easiest way to check this measurement is with calipers.  This measurement is taken on the slide at the widest point of the dovetail, front-to-back. It may be hard to get an exact measurement, but it should be easy to tell whether your measurement comes close to one or the other of the above examples. 

Measure from the front of the slide to the approximate center of the dovetail. Again, it may be hard to get an exact measurement but you should be able to tell if it’s closer to either 0.250 or 0.320.  



Measuring the dovetail cut

Now measure the depth of the dovetail – hopefully it’s either 0.075 or 0.060.  Only one more measurement and you are done. 

Measure the height of your front sight.  You want the height of the sight on the end furthest from the muzzle.  Measure from the top of the blade to the top of the slide.

If you are happy with how your gun is sighted in then you want to get a sight that has the same height as the one presently on your gun.  If you want to change heights, you will have to do a little calculation to figure out what you need. To determine how much a change in front sight height will alter your point of impact, do the following calculation: divide the distance to the target in inches (at your desired sight-in distance) by your sight radius in inches.  Take the resulting factor and multiply it by the change in sight height.  This gives you change in impact.  For example, if your gun has a 6-inch sight radius and you are sighting in at 25 yards, your factor would be 150 (900/6). If you change your sight height 0.010, your point of impact will change 1.5 inches (0.010 x 150). Armed with these measurements, you can now choose your sight from those available with a dovetail cut that matches your slide.

Once you have chosen your sight, it is time to install it.  Begin the installation process by removing your old sight.  Cover your slide with masking tape to protect the finish. Then put the slide in a padded vise. Check to see if the sight is being held in by a pin.  If it is, remove the pin before you continue.  To remove the sight, use a brass punch to knock it out of the dovetail.

If you had a mill, you would continue by measuring your dovetail with pins and calculating its width.  You would then measure your sight the same way, flip it over, and cut it to size with the proper dovetail.

Measure dovetail with mill Measuring the sight


However, since you likely do not have a mill or the proper tools to measure the dovetail, you are going to have to do it the hard way.  Begin by prepping the dovetail cut in the slide by knocking the sharp edges off the top of the dovetail cut with a file.  You want around a 0.010 flat on these edges so they don’t cut into the sight and create a stress riser that could crack or break the sight. 

 Preparing the dovetail

To compensate for sloppy tolerances in the dovetail cuts of many slides out there, most manufacturers actually machine their sights a little larger than the measurements stated on the package.  For example, the Lightning Rod sights we manufacture that are listed as 0.330 wide are actually 0.335 wide.  This means you may have to cut the sight back a little to fit in the dovetail. We want the sight to fit tight, not loose.  The easiest way to fit the oversize sight is to file or sand a little material off the bottom of the sight. This will have the effect of bringing both sides of the dovetail in a little.  I recommend this method rather than trying to file material off the sides of the dovetail because it is hard to match the angle and take even amounts of material off the sides.  Be careful to keep the bottom of the sight square as you file. 

Fitting the sight

File and fit until the sight just starts to go into the dovetail. You want the sight to be snug but you don’t want to have to knock it in with so much force that you damage the sight.  Always hit the side of the dovetail and not the blade.  If you strike the blade, you might bend it. Once the sight starts to go into the dovetail put a little bit of red Locktite in the dovetail and start to tap the sight into place.  As the sight enters the dovetail and gets closer to the center, check that the bottom of the blade is not hitting the top of the slide.  If it is, remove the sight and take a little more off the bottom of the blade until it clears the top of the slide. Zero clearance under the sight blade could put pressure on it and could cause it to break.  Now measure to be sure your sight is centered in the slide, and you are done.

Wrap up the process by sighting in the gun at the chosen distance.  If your calculations were spot on, you are ready to enjoy your new sights.

 1911 parts at Brazos Custom