Birmingham Black powder proof marks, Pre 1904,for 11G bore size [Bore diameter should measure between.751 -.762 inches to still be in proof.]Chamber size will determine whether the gun was made as a 12G or a 10 G. Weight of the gun will also be a clue as to its design size.My opinion is that it is likely to be 10G because many guns of this vintage,[pre the introduction of choke boring] were bored one gauge smaller than nominal [ie; many 12G guns of this vintage were bored and proof tested at 13G.], I think that the objective was to improve pattern density.Others have suggested it was a wear allowance to allow for a future reproof of damacus/twist barrels.Recommend that you have a gunsmith measure the chamber size and compare results with the dimensions specified in the relevant rules of proof.
Last edited by Roy Hebbes; 02/06/10 06:14 PM.
