Roy Dunlap's book "Gunsmithing" has minimum chamber & Maximum Shell dimensions for the common shotshells in use at the time of publication (Copyright dates of 1950 & 1963, 2nd edition). I presume these to be SAAMI Specs, but he does not positively state their source. For the 2 3/4" 12ga minimum dia at end of chamber is given as .798" to a point 2.6136" from the breech face. Note this is a bit shorter than the 2.625 of a 2 5/8" chamber. A minimum dia of .764 is given in the cone at 2.8079" from the breech, or about .05" beyond 2 3/4". For the shells a max length is given for roll crimp shells of 2.53" & for folded crimp of 2.41. A max fired length is given for both of 2.760" Note that the max loaded length of either crimp type does not reach the forcing cone allowing unrestricted opening of the crimp. "THIS IS IMPORTANT". Note also that all other gauges have the minimum chamber length at least equal to the nominal shell length, only the 2 3/4" 12ga shows a shorter chamber.
To the best of my knowledge both Bell & Burrard had the same thing to sell, their writing. As stated in my previous post though most of Burrards reporting on this issue was of tests carried out by the British Ammo trade who did have something to sell. This however is not necessarily bad. Remember also when we are speaking of the British their shells had to meet the approval of the proof houses, so yes they had to test a new concept prior to placing it on the market.
Right or wrong the top wad got blamed for "Bad Patterns". With the switch to the fold crimp the British shotshell makers were immediatly faced with two problems. 1st bulk powders were still quite popular there & to put the normal load into a hull now having reduced capacity due to the extra length taken up by the crimp made it diffucult to have an efficient wad column. 2nd the shorter overall length of the hull could be quite easily mastaken for a 2" shell once removed from its original box.
The result was they began experimenting with putting the normal load in a longer case which would have about the same overall length when loaded. It was not at that point in time desirable to lengthen the chambers as this would have required proofing for the heavier load of the regular 2 3/4" shell. "VERY" extensive tests were performed & it was determined that when the proper load was put up in the longer hull no problems resulted from the practise. These tests began in the late 1930s were interuppted by WWII & were definitely finished by the end of the 1940s. The pratise of putting a proper load for the gun in a hull slightly longer than its chamber has thus been well established for more than 60 Years. Anyone can accept it or not as they choose, but it does require ignoring a lot of "Facts".
As to US guns I believe it was mostly Trap shooters who desired the 1/8" short chambers in their guns. It was not a universal practise among US gunmakers to habitually chamber their guns 1/8" short of the noted shell length, but some did, at least for 2 3/4" shells. As during this ers I believe the majority of US Trap shooters preferred the 2 3/4" shell & as most gunmakers of the era would chamber guns to order those desiring to use 2 3/4" shells in a 2 5/8" chamber could have simply ordered their gun so chambered if this was not the practise of the desired gunmaker.
I do recall Bell testing 3" shells in a 2˝" chamber just to see what would happen should he leave one in his pocket & accidently insert it into one of his 2˝" chambered guns. The load did raise the pressure a good bit but he decided it would not result in a catastrophy. The load however was a very light one for a 3" shell, so much so in fact it made one wonder why he bothered with the longer hull to begin with. I apparently missed the issue in which he tested 3" laods near SAAMI max in a 2˝" chamber. I personally would try My Hardest to keep a 3" shell loaded to Near SAAMI out of any 2˝" gun I have or should acquire, even if it wasn't likely to actually "Blow it UP".
