There is an easy answer if the gun is in proof: sell it in the UK.

First, I would add my second to the thought that a re-measurement is in order. Those walls are not impossibly thin but I would also like to know if these are the original barrels. If so, phone H&H and find out the original dimensions...this may have been a light game gun I suppose.

Where on the barrel is the spot and how big is it?