In that condition the proof house would not permit it to be proofed; it would fail view. A 12 bore usually, if no modifications to chamber length or certain other factors have altered the gun, is deemed out of proof if the internal barrel measurment at 9 inch from the breech face has increased by more than 10/1000 inch to the marks stamped on the barrel. Looking at it I think that it has reached the 'scrapper' status. Not a particularly good specimen and the cost involved of returning it to being a shooter would far exceed its worth. Just an interesting piece of history at a guess. Lagopus.....
