FWB Modell 65 Variable Aperture Front Site

I've owned this from production, new 

This was built for me at the request of Robert Beeman (who I knew personally, as well as his dear wife, and others who worked there).

I'm seeking info on the front site, that was installed as new when the pistol was produced.

The front site has a continuously variable front aperture, post width is adjusted via the ring around the barrel.

It works flawless I have all original paperwork onton the pistol, I would just like some detail literature on the sight, if it's out there?

I don't see many configured this way thought I would ask here, thank you.

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