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.

Generally, yes, but not definitively. I have seen and measured 3 British guns with 2 1/2" chambers and 1 1/4 oz. proofmarks. All of the guns stamped 1 1/8 oz. that I have measured had 2 1/2" chambers though.

My findings are pretty much as Blue Grouse,some W.W.Greener 2&1/2" guns have 1&1/4oz load marks.

Larry, also they sometimes make mistakes and pick up the wrong punch. I had a Thomas Wild hammer pigeon trap gun with nominal bore not marked so it was impossible to say whether it was in proof or not. I sent it off for re-proof to get it clarified. Sometimes in that era you referred to and before the chamber length was sometimes stamped on the forend lump by the maker. Along with Hugh, I have seen this on Greener GP guns. Lagopus.....

The British Proof houses operate on a simple two rule system,

Rule one . The proof can not be wrong make mistakes , their word is final.

Rule two , If it can be shown/proven that beyond all doubt the Proof House is or could be in error , see rule one .

Having dealt with both Proof Houses this joke is pretty close to true . That said errors do occur always have and always will.

Any organisation that has been in existence for so long and undergone so many changes in rules and specifications will have some areas that will always be debatable especially in years pre and post change .New stamps issued prior to a change may and have been used in advance of the official change over date .Imperial to metric for example .

As British Proof Law does not apply in the US it is all academic , guns get altered and rumor has it there several sets of British " proof stamps" in the US .So who knows ?

Gunman, it seems to me that it matters to us on this side of the pond if we have a pre-1925 gun, 1 1/8 oz proof and 2 3/4" chambers which do not appear to have been altered.