In the late 1890s and early 1900s our ammunition companies were offering smokeless powder loads up to 3 1/4 drams and 1 1/4 ounce of shot in 2 5/8 inch paper 12-gauge shells. It seems that between 1903 and 1910, 1 1/4 ounce loads in 2 5/8 inch shells disappeared from their offerings, and from then on only 1 1/8 ounce and lighter loads were offered in the 2 5/8 inch case and one had to go to 2 3/4 inch or longer 12-gauge shells for 1 1/4 ounce loads. Up to April 1940, the ATA allowed up to 1 1/4 ounce loads and lots of shooters used them. For at least 20 years Western Cartridge Co. offered a 12-gauge 3-inch Super-X Live Pigeon or Handicap Trap Lubaloy load with 1 1/4 ounce of 7 or 7 1/2. At various times both Peters and Remington offered such loads as well. I have seen some A.H. Fox Gun Co. production cards that state the customer wanted his gun chambered for 2 5/8 inch shells, but I've never had a chance to actually measure the chambers of such a gun. For those of you who are A.H. Fox Collectors Association, Inc. members, check the archives for the April 2011 Card of the Month, an XE-Grade two-barrel set with the long barrels ordered chambered for 2 3/4 inch shells and the shorter set for 2 5/8 inch shells.
In the days of two-piece shell boxes it seems that when the length wasn't stated on the label they were 2 5/8 inch shells, while the longer 2 3/4, 2 7/8, 3 and 3 1/4 inch shells were identified on the label. In one-piece boxes the 2 5/8 inch are often identified.
All of our North American ammunition companies continued to offer 2 5/8 inch 12-gauge shells and 2 1/2 inch 20-gauge shells up to WW-II, while the 2 9/16 inch 16-gauge shells were offered into the early 1960s. Here is a 1934-39 style Remington SHUR SHOT box of 2 5/8 inch 12-gauge shells --
Threaded Mode