Fiatcrew,

I just looked at the Chapuis sight, and I don't see the "S12" or "C10S" listed anymore. This was the O/U version of the adjustable regulation system. A man on another forum has indicated he has a Chapuis SxS with the same adjustable system. But they may have dropped this since they were acquired by Beretta. But you may still find them out in the wild.

Anyway, some of the German double rifle makers offered a similar system also. Maybe Krieghoff and Blaser? Hopefully somebody who knows will chime in.