OK now this is gun smith work.Doing some guess work making this spring for the Cooper. The cylinder stop spring and screw were missing and I had no idea what they look like. No diagrams available so I'm going by what will fill the missing space and hope it works. Need to pick up a 6-32 screw and grind the head down to fit, there been a lot of file/fit work with this one.
The trigger return spring View attachment 154573on the left is just a V spring, but cylinder stop spring on the right doesn't have much room to move up and down so I made it from thicker steel. It has to put tension on the cylinder stop, but not too much or the cylinder stop release will ride over the bottom of it and I'll have to take the revolver apart every time I want to remove the cylinder to clean it.
A lot of this is just taking a gun partially apart and working the mechanism with your fingers.