FOX CHAMBERS --
The only two A.H. Fox Gun Co. catalogues, that I have seen, that state chamber lengths are the 1913 and 1914. From the 1914 A.H. Fox Gun Co. catalogue --
They both state 12-gauge guns are regularly chambered for 2 3/4 - inch shells, 16-gauge 2 9/16 inch shells and 20-gauge 2 1/2 - inch shells. That being said, virtually every 12-gauge Ansley H. Fox gun made in Philadelphia (other than the HE-Grade Super-Fox) that I've run a chamber gauge in shows about 2 5/8 - inch. The chambers of unmolested 16-gauge guns seem to run about 2 7/16 inch and 20-gauge guns a hair over 2 3/8 inch. A very few graded guns were ordered with longer chambers. Savage began stating chambered for 2 inch shells in their 1938 Fox catalogues.
All this being said there is a good body of evidence that back in those days chambers were held about 1/8 inch shorter than the shells for which they were intended. In the two-volume set
The Parker Story the Remington vintage specification sheets on pages 164 to 169 call for a chamber 1/8-inch shorter than the shell for which it is intended. Also in the 1930's there were a couple of articles in
The American Rifleman (July 1936 and March 1938) on the virtue of short chambers. Sherman Bells articles in
The Double Gun Journal covered his tests showing no significant increase in pressure from shooting shells in slightly short chambers. IMHO I don't much sweat that 1/8-inch in 12-gauge guns. On the other hand when one gets a 20-gauge chambered at 2 3/8-inch likely intended for 2 1/2-inch shells I do worry about folks firing 2 3/4-inch shells in such guns.