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Building A 1911 - Part IV

By: Mike Watkins

This time we’ll cover the installation of sights on your slide. There are a ton of options from fixed sights to adjustable ones out there. If you are using a slide with fixed sight cuts already in the slide and a stake on or a dovetail front sight, only minor fitting of the sights you have chosen could be required. Some of you may have ordered your slide with a Bo-Mar rear cut and a dovetail front; again only fitting the sights are needed with drilling the elevation screw hole and tapping it for the elevation screw on the rear sight.


Take a look in the latest Brownells Catalog and you’ll find that there are lots of options for fixed sights, night sights, and adjustable sights. For my project, I decided to install a Bo-Mar adjustable sight for the rear and an EGW dovetail front on this pistol.

I know the proper machinist method is to locate zeros with an edge finder and then figure the amount of table movement required for each cut you are doing. I still scribe layout lines on the part and use those as a means to double check my calculations. If the phone rings and you only crank the handle twice instead of the required three, it’s easy to see before you make a cut and ruin a $200.00 part!

The Bo-Mar BMCS will be a Lo-mount installation since I really like these. After shooting pistols with this sight for over 30 years in competition, I’m quite used to the sight picture. Remember, I said everyone has his or her own preference! These just happen to be mine.

Before machining the slide be sure to measure your BMCS Bo-Mar sight as they vary a little from sight to sight. You may have to adjust these dimensions for your sight!!


Coat the top rear of your slide with layout blue or paint it black with a permanent marker so you can scribe reference lines on it for machining the cuts needed. From the breech face, measure back 1 inch and scribe a line, this will be the forward stop point when you machine the flat on the rear of the slide and remove the factory dovetail. I use a 3/8”, 4-flute end mill and just touch the bottom of the original fixed sight dovetail on the rear of the slide. You will then mill a flat the full width of the slide up to the one-inch mark you previously scribed onto the slide. If your slide doesn’t have a dovetail in it, lower the end mill down 1/10” for that cut. After that flat is machined, measure from the edge of the one inch mark .480 thousands to the rear of the slide and scribe another mark. This will be the center line for your new dovetail. Use a pointed center finder to locate the center of the spindle to that center line, and lock the mill table down so it won’t move.

Remove the center finder and install the correct dovetail cutter for your sight, usually the Bo-Mar Rear Sight Dovetail Cutter. Raise the mill table up so the dovetail cutter just touches the slide, move the slide from under the cutter and raise the mill table up approximately 1/10” for the dovetail cut. Again, measure your sight since they do vary some!!

I made a full pass with the dovetail cutter, which made an undersize cut. Then, I measured the width of the sights dovetail and determined how much more will have to be cut to widen the dovetail to fit the sight. I moved the cutter to the rear of the dovetail and made the second cut about .005 thousands of an inch smaller than needed. Next, I trial fitted the sight to the dovetail to see if another cut was required. If all has gone well it should just start into the new dovetail and if it does, use a Safe Edge Triangle File for the final fit and to smooth up any machine marks.

With the sight installed in the dovetail, measure and center it from side to side. Mark the center of elevation screw hole. Then lower the sight blade down against the slide and scribe a line around the sides and rear of the sight to locate the sides of the relief pocket for the sight to go down into. You will also scribe a line for the forward edge of the pocket, raise the sight up and then use rear edge of the sight base to locate how far to machine the pocket cut forward. I don’t make the circular cut for the windage screw on the right side, just my preference as I think it looks better without that cut and once the windage is set I vary seldom have to readjust for windage.

Remove the sight from the slide and cut out the material for the relief pocket approximately .135 thousands deep with a 1/8 inch 4F End mill. The rear of the slide will also have to be relieved for the sight blade to clear the side shields. This cut will be about .080 thousands forward of the rear edge of the slide. Refer to the drawing.

Now you can center a # 31 drill for the elevation screw, with the center mark you made before and drill that hole into the slide. It will be tapped 6/48 TPI with a taper tap. I drilled that hole through into the firing pin tunnel and then deburred it later on. With this done you can reinstall the rear sight in the slide and check the fit of the sight blade body in the relief pocket.

Now we can cut the dovetail for the front sight, if required. Or, fit the sight to your slide if that cut has already been done. You may have a stake on front and need only to fit the sight tenon to the slide and grind a relief into the inside of the slide where the tenon comes through. This will provide a relief for the tenon to flare out into like a rivet head and better secure the sight. Then, lightly file down that “rivet “to clear the barrel bushing.

For my front sight I have chosen the EGW Fiber Optic Front Sight. It comes with two inserts; a green and a red. I like the red insert for my old eyes, better than a new pair of glasses!

This sight is listed to be a .330 X 65 degree dovetail with a thickness of .070 inches; measure the one you have in your hand to be sure. Mine actually measured .3365 inches wide for the dovetail and .0755 inches thick.

Now you will have to determine the centerline for your front sight. With a dial caliber you can measure from the front of the sight blade to the edge of the dovetail. The one I have is .1515 inches and after adding in half of the actual width of the dovetail, for my sight that is .1682 inches. This adds up to a total of .319 inches rearward from the face of the slide. I set my dial calibers to this measurement and held it up to the front sight and gave it the calibrated eyeball to double-check myself. Then, scribe that line on the slide and use a pointed center finder to locate the center of the spindle to that mark.

Install the correct Dovetail Cutter (this specific cutter works on my sight) and raise up the mill table for the proper depth, on my sight that is .075 of an inch and machine the dovetail for the front sight. A small triangle needle file will remove tool marks and be used for the final fitting. I will hand fit until the sight will go into the dovetail about a ¼ of an inch, coat with Red Loctite, and tap in with a Nylon Punch, once the sight is in place and centered for windage, I can install the red fiber optic rod with a touch of superglue and I’m done. Now we can go to the range and have some fun!

Next time we will cover fitting of the trigger/hammer components, see you then!

Building A 1911 - Part V