Proof diameters are measured and apply only at a point 9 inches from the breech.A 13G OR 13/1 gun would be deemed in proof upto.728 diameter maximum.When the size reached .729 diameter the right barrel would be declared," out of proof" and would require reproof as a 12G. In so far as the larger diameter measured at the muzzle of the right barrel; this could be an attempt by the manufacture or some other at a later time to increase the shot spread.
There should be included in the proof marks on the barrels, a stamped diamond, inside of which will be found the symbol 12/C. this is the mark that confirms the gun was chambered for 2 1/2 shells. If the diamond includes the symbol 12/LC the gun was chambered for shells longer than 2 1/2. Frankly I will be surprised if this is anything but a 2 1/2 chambered gun. So many time I have seen old guns rendered out of proof because the chambers have been extended.[Some old time gun smiths thought that by increasing chamber length they made the barrels/gun safe for shooting 2 3/4+ shells,instead they rendered the gun "Out of proof"!]
Last edited by Roy Hebbes; 07/05/09 09:05 AM.
