The long ARROW 12-gauge shells offered by UMC in 1905. With bulk smokeless powders, DuPont, E.C., Schultze, etc. --

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With dense smokeless powders, Ballistite or Infallible --

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The standard chambering for Philadelphia Arms Co. was 2 5/8-inch (likely intended for 2 3/4-inch shells), but they would chamber for longer shells if the customer requested. Recommended loads from the 1905 Philadelphia Arms Co. catalog --

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The only two A.H. Fox Gun Co. catalogs that mention chamber length are the 1913 and 1914. 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 ¾- 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 book 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. A series by Sherman Bell in The Double Gun Journal showed no significant increase in pressure from shooting shells in slightly short chambers.