Prior to the 1925 proof rules, chamber length was only marked on guns under very unusual conditions. With that rule change, chamber length became a required proofmark. However, under the 1904 rules, shot charge was a required mark. Can we state definitively that all 12ga guns marked 1 1/8 oz had 2 1/2" chambers and all of those marked 1 1/4 oz had 2 3/4" chambers? Thanks.