Bill,

I looked at the 586 very closely with my eye and light source at different angles. At first, all I could see was the surface of what looked like monolithic barrel with sight then, on the left side I could make out the full circumference of a pin outline. The pin is absolutely flush with the surface, the entire surface has been abrasively polished to appear uniform.

I'm not going to tackle this myself but now I have defined the scope of the project: Remove existing pinned sight then install new fiber optic.

Thanks for your help!