Retro Rear Sight Installation Tips
I get a lot of slides sent to me for the installation of H-D sights and a many of those are for my Retro rear sight. Since my goal is usually just a simple sight installation with no refinishing in the game plan, I try to do all modification in a manner that will preserve the exterior finish of the sight. Typically, the dovetail on the new sight is too wide to fit in the slide’s dovetail, so I remove material from the bottom of the sight’s dovetail which makes the sight narrower. Some guns can need as much as .008" or .010” removed from the bottom of the sight to make the sight fit the dovetail’s width. That's actually a lot of filing & sanding to remove this much and it’s pretty hard to remove this much material and keep the new surface in plane and true with the original one.
I measure the width of the old sight and the width new sight across “rolls” using a dovetail measuring fixture made by XS Sights and available from Brownells. Subtracting will give the theoretical difference in width between the two sights. If you just measure across the dovetail between the jaws on your caliper to the points you will likely not get an accurate measurement, due to the bevel that is normally cut across the tip of the dovetail. I make an initial cut from the bottom of the sight of about 60% of the measured difference using my milling machine. I made a small aluminum jig to let me hold the sight upside down, square and level in my vise jaws, with the sight raised up enough above the jaws to give me room to make the cut.
After the initial cut is made, I bevel the bottom front & rear corner of the sight and attempt to start the sight in the dovetail. If the sight won’t start in the dovetail and more material needs to be removed, I lay a coarse mill bastard file on my workbench and stroke the sight down the length of the file. I stroke only in the direction that the file normally cuts, holding the sight so the longest surface is in the direction of the stroke, being careful to not tip the sight over and scratch the sights exterior surfaces that we want to preserve the bluing on. Every couple of strokes I reverse the sight to the file, to keep from cutting more from one end than the other. If you don’t have a mill, this is how you’ll have to take off the entire excess material.
Frequent checks of the fit in the slide will tell you when it's time to try to drift it in the dovetail. I use a 10x magnifier to look into the joint, while holding the slide so that a strong light source is behind it. This way, I can see if the sight has any gaps in its fit with the dovetail. If you were to have a gap at the bottom, you likely need to file larger bevels on the sight’s bottom corners. If I can get the sight to go in about 1/4 of the way with just a couple of light taps from a non-marring hammer and I don’t have any large gaps, then I'm close enough to try drifting in in the rest of the way. Before I do, if I’m installing a Retro, I use a flat needle file and carefully file a small bevel on the upper edges of the slide’s dovetail to reduce the chance that the sight will be scratched as it’s drifted in. As I’m drifting it in, should the rate of movement slow, I stop drifting right away and knock it back out. Look at the dovetail surfaces with a magnifier and see if you find galling and if so, take another stroke or two on the file and try again. Use patience as much as you use your file as it is easy to go too far and get a loose fit. Hope this helps!