Thanks Researcher, I was not sure of Fox's policy on chamber length, some US makers did tend to cut them 1/8" short while others didn't. All of my Lefevers check out at nominal either 2 5/8" for the earlier ones or 2 3/4" for the later ones in 12 gauge, my one 16 gauges has a full 2 3/4" chamber, even though 2 9/16" would have been standard for the day. L C Smith drawing specs show 20 = 2˝", 16 = 2 9/16", 12 =.2 3/4" & 10 = 2 7/8".
In Roy Dunlap's book Gunsmithing he shows SAAMI specs for chamber dimensions. In 12 ga only is min chamber called shorter than max shell length. It is there called a bit less than 2 5/8", as I recall about 2.618" for the nominal 2 3/4" shell. It was my understand these shorter chambers had been the result of request by trap shooters, so was not certain they had ever been applied to gauges other than the 12 or not.