There are a few misconceptions here concerning proof/reproof. Mr. Barclay didn't mention whether the gun had been reproofed previously at some time. However, although it's much more likely the gun started life as a 2 1/2" gun, we don't know that for sure. But since the proofhouse tag says 12/70, then that's either what it was to start with, or else--somewhere along the line--it had already passed one reproof with the lengthened chambers. Otherwise, it would not have been a case of whether Toby WANTED to have it reproofed just to be on the safe side. If the chambers were lengthened from 2 1/2" to 2 3/4" and the gun had not been reproofed, then it would be illegal for him to sell it without submitting it for reproof.
You won't find chamber length marked on 1880's guns unless the gun has been reproofed. Chamber length wasn't a required proofmark until 1925.
As for the pressure of a current reproof, it is my understanding that even a 2 3/4" gun, if the owner so requests, can be proofed at the "standard" level (rather than the much higher superior proof level). Per the Birmingham Proofhouse, that is something a bit less than 14,000 psi as we'd measure it in this country. British/CIP standard proof guns use shotshells that generate pressures of slightly less than 11,000 psi. So while a standard proof load is indeed an overload, there isn't nearly as much of an overload as there is between the standard service pressures of American shotshells and the pressures of American proof loads. 12ga SAAMI service pressure is 11,500 psi, against a proof pressure of something in the 18-19,000 range.
Current British proofmarks are pretty clear. If the gun is standard proof, it's marked STD--and you use the shells suitable for a standard proof gun. If it's superior, the marking is SUP--and hotter American shotshells will work just fine. Older British proofmarks can be somewhat confusing unless you know how to decipher them.
Last edited by L. Brown; 07/31/17 01:33 PM.
