Join Date: Sep 2008
Location: Bavaria, Germany - the center of 15th and 16th century gunmaking
There was not a pin but a screw thread soldered to the underside of the belt hook or made out of an iron pin rivited there. Of the two holes in the horn, I guess the upper was the original one. Just take out the top mount transverse screw and take off the belt hook and you should find the remains of the thread.
At the same time please screw off the side cord rings, take off the top mount and look inside whether the horizontally moving cut-off plate is still riveted there. You should also find greenspan from the copper soldering processs.
Was there ever powder in your flask?
Please take good images of the inside and show us! The outcome would be highly interesting.