Installing a Mini Red Dot Mounting Plate on a Smith and Wesson Revolver (586/686)

Drill and Tap Smith and Wesson Revolver finished

My first experience with red dot sights was back in 1996. I was a Marine Corporal working as a range liaison in MCAGCC 29 Palms California, when an Army Special Mission Unit let me shoot its M2 and MAG58 machine guns which were equipped with Aimpoint 2000s. I thought they were neat back then, little did I know that red dot optics would become common place. Unlike traditional iron sights, which have three planes to align, red dots have one. In addition to being “easier” to use than iron sights, shooters with aging eyes often find them necessary to stay in the sport. In this post, let’s look at how I install a red dot mounting plate on a customer’s Smith and Wesson 586 Revolver.

Installation of this plate requires drilling and tapping the top strap of this L-frame revolver. I believe, on later models, the holes may already be in place, but in this case real gunsmithing is required. Unlike some projects, I don’t consider this one especially difficult. The three holes I have to drill and tap are all through-holes, no blind holes to risk breaking a tap in. While I will do this on a mill, I think with a proper set up, I’d be able to pull it off on a drill press without getting too nervous.

Before we get to the work, please take a look at the following disclaimer:

The contents of Rifleshooter.com are produced for informational purposes only and should be performed by competent gunsmiths only. Rifleshooter.com and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

Any modifications made to a firearm should be made by a licensed gunsmith. Failure to do so may void warranties and result in an unsafe firearm and may cause injury or death.

Modifications to a firearm may result in personal injury or death, cause the firearm to not function properly, or malfunction, and cause the firearm to become unsafe.

I ordered the base and the following tools and parts from Brownells to complete this project:

I begin by making sure the revolver is safe and empty. Then I remove the cylinder and yolk to get them out of the way. To do this, I simply remove the yolk screw located in front of the trigger on the right side of the frame, open the cylinder and slide them both forward.

Next I need to remove the adjustable rear sight from the 586. This is facilitated with the removal of one screw. I like to use professional gunsmithing screwdrivers with a flat non-tapered tip. Brownells Magna-Tip insert bits have always worked well for me.

With the screw removed, the rear sight simply comes off. Now I can lay out the holes for the mount.

This is the ALLCHIN mount mocked up in place. This is a one-time job for me, and since they didn’t include a drawing with dimensions, I’m going to use a transfer punch to mark the locations of the three holes that I’ll need to drill. A transfer punch is a hardened steel tool that matches the diameter of the hole you are trying to locate. The end of the punch has a sharp tip. You simply place it in the hole you are locating and tap it to leave a mark.

This image shows the transfer punch on the top strap. If you look closely you may see the location marks.

I decided to drill and tap these holes on the milling machine. Work-holding on most guns and gun parts can be a challenge, on a revolver, that task can be extra difficult. I ended up holding the sides of the barrel in the milling machine’s vise with a set of bronze jaws (to protect the barrel) and leveling the revolver in both the X and Y-axis with a Starrett cross test level. I find this tool essential for jobs like this.

Next, I use a center finder to locate the centerline of the top strap of the revolver. If you look closely in this image you can see the three bright marks that denote the locations of the holes for the mounting plate.

Next, I use the a tool called an “NC SPOTTER” to spot, or start each one of the holes. This helps prevents the drill bit from deflecting when I drill the holes.

I like to use cobalt split-point drill bits to make my holes. Cobalt bits are less expensive than carbide, work both in manual and CNC machines and are usually readily available at most tooling suppliers. The split-point bits tend to walk less than traditional bits, keeping your holes in the right spot.

Since I have the revolver already held in the mill, I decided to use a tap guide to help ensure the tap goes in perpendicular to the top of the frame. I really like these guides, especially for precise work like this.

I always like to take a few minutes to admire my work. These holes look professional! Unfortunately, they’ll never be seen under the mount!

Before I move to final assembly, I take a few quick passes with a stone along the bottom edge of the top strap. This removes any burrs that were caused by the drill bit or tap passing through.