Beautiful M/S !
They are just top notch rifles and carbines IMHO
Isn't that called a Diopter sight ?..intended to make the sight picture of the bbl and front sight much clearer to the shooter.
Pin-Hole' sight it is sometimes called as well when meant to do the same task. Some Bullseye pistol shooters used to have a simple disc shaped one clamped to their shooting glasses to help them better focus on the iron sights.
I have a scaled down version make believe M/S with one fitted to it. Another project gun..
