Got some work done on the project the last few days in isolation, moatly on the rear sight and mount.
I did pick out a stock blank to use, have a look below

I liked the mineral lines and colour of this particular one.
I started my work on the sight base. As noted before, this was a military bridge, so it had a charger guide that was cut off at some point in its past. It was pretty well done, but has some rough cut lines, so I cleaned those up. This part will be reblued when the time comes. I just used a mill file to clean it up, then wrapped the file in some wet dry sandpaper to polish the surface up to 600 grit. One of the things to be sure to do if you ever do this is to ensure you file the excess metal to the cove shape the side of the bridge has. I used a dowel wrapped in wet dry for this part.
Next is the sight itself. I decided to do a mechanical rebuild and leave the finish alone since it is in pretty good shape. I am only doing what needs to be done to bring it back to usable condition. I may add an eyecup at a later date as the hole is abysmally tiny, but I have to make sure it will clear the bolt first so I can find something the right diameter.
Got the sight broken down. I should have two of both of those screws and another one of those latch parts with a spring:
I have to make another one of these parts. It has an open ended threaded section that the spring pushes against a screw to allow the slider to move up and down. I decided instead of making the new one for a V spring, I would design it for a small coil.
The thread needed was a 0.5 pitch, so I found I had a 3mm-0.5 tap on hand that would work. It's not exact, but for the short mating surface it works very well.
I used an old moulding plane iron that is quite soft, and is about 20 thou thicker than needed for the part
I used some sharpie to trace out the rough shape of the part
I want to do as much machine work as possible while it is still a large piece of metal. It makes it easier to clamp and work with. Here you see me marking the location of the pivot hole with a punch. You can also see the punch mark I made on the end where I would drill and tap for the threaded portion. In hindsight, the saw cut you see I would have made after. I made this so I could remove chips more easily when tapping and see my depth, though this wasn't needed.
Tapping the hole:
Next I must apologize, I didn't take any pictures of shaping the part with the file. This stage was just filing to shape, rounding edges to match the original, and drilling a small hole in the back to accept the coil spring. I also trimmed the replacement bolts and cold blued all the parts to match the finish of the sight.
Last is an assembled and greased BSA pre-Martin target sight

Function is a little tight in places so that needs to be addressed, but I should be able to get it working flawlessly soon.
In other news, my stock ***should*** be on the duplicator this week, and the barrel blank also ****should**** be done this week. Once the stock arrives I can get working on final shaping and contouring, as well as some detail work before the action arrives for inletting.
Talk soon!