Clif W.The proof marks seen on your gun are those normally found on 2 1/2 inch chambered, English 20 gauge guns.Based on your comments there is little doubt that a mix-up occured at some place in the ordering, manufacturing or even as others have suggested at the proof house. My opinion is that the gun was made with 2 1/2 inch chambers and that the error was not discovered until the gun was delivered to the origional owner in the U.S.A. At that time a decision was made to extend the chambers to 2 3/4 and as part of that process that the new chamber length 2 3/4 was stamped on barrels. It should be noted that; no change was made to the maximum allowable shot charge[ie;increasing it from 7/8 to 1 ozs.].
During this era many English guns imported into the U.S.A arrived with 2 1/2 chambers.Chambers of these guns was frequently extended to 2 3/4 without regard to the English rules of proof.In my experience more than half of the English guns I have encountered over the past 40 years have had the chambers extended and have never been submited for English reproof.
