Are you looking at that round area which shifts when opened? That is part of the locking system. Take a look a Greeners for clear examples.
Welcome to the club. Fair warning, doubles can be addictive and costly. Buy quality, not the name or shine. Most A&D boxlocks are the same, with a majority made by a few makers not necessarily the names on the gun. Bringing in semi or completely finished gun and having your name on them, like you built them in house, is a long standing and completely acceptable thing in the trade.
tallen72,
If you are talking about the round disk it if the end of the cross bolt. It goes thru a hole in the rib extension & is most likely tapered. This locks the action closed and is controlled by the lever, when the lever is moved to the right it moves the cross bolt to the left unlocking the action allowing the barrels to drop.
Hope this helps.
WBLDon
Thank you both. I have a couple of American doubles from the 20s and then a French guild gun from the interwar period, but none of them are Greener actions, so I had not seen this before.
The gun in question is a John Robertson from Boss & Co. bearing the 41 Albemarle Street London W.1 address.
