Caprivi, the pin is fitted from the top. It is a finely threaded screw with an hardened teton on one side and a 45° angled head. The hole pierced in the bridge is treaded and a 60° bevel is machined, then the screw is heavily seated in, forcing the existing cone to open, so when carefully filed it disappears.
The joke is to put the pin at the right place !
On the photographed action there is zero play to the shroud and cocking piece when closed...perhaps some luck.
John303, when I say that small ring actions are rarely encountered, I speak about Original Oberndorf civilian ones. Here, on that side of Atlantic, I have seen much more kurz or magnum Oberndorf actions than SR.
But it's my point of view only.
Thanks for your interest.

DORLEAC
www.dorleac-dorleac.com