At the time 1518 was made, our North American ammunition companies were offering loaded 12-gauge paper shells in 2 5/8, 2 3/4, 2 7/8 and 3-inch lengths. Popular new shotguns of the time like Remington's John M. Browning designed Remington Autoloading shotgun and their John D. Pedersen designed Remington Repeating Shotgun and Winchesters Model 1897 were made for 2 3/4 inch 12-gauge shells.
One and 1 1/8 ounce loads were offered in the 2 5/8 inch shell and the 1 1/4 ounce loads were offered in the 2 3/4 inch and longer shells. In those days, the longer 2 7/8 and 3-inch shells didn't carry heavier loads than were offered in the 2 3/4 inch shells, but offered more/better wadding which many serious trap and live pigeon shooters believed important. The heaviest 12-gauge loads offered from the late 1890s to the early 1920s, 3 1/2 drams of bulk smokeless powder or 28-grains of dense smokeless powders such as Infallible or Ballistite pushing 1 1/4 ounces of shot produced higher pressures then modern SAAMI specs. The high velocity, progressive burning powder, loads were still thirteen years in the future when 1518 was built.
The Royal Gun Co. catalog states on page 12 --
Shot barrels are bored on the latest improved taper system for shooting all grades of smokeless powder.
I can't find any mention of shot barrel chamber length in any of my Hollenbeck, Three-Barrel or Royal Gun Co. catalogs. The hang tag for 1771 a Grade 2, 12 x 12 x.25-35, lists the load it was targeted with as 3 1/8 drams of bulk smokeless pushing 1 1/4 ounce of #7 1/2 shot, a very popular trap load until the ATA limited loads to 1 1/8 ounce beginning April 1940. Our North American ammunition companies were only offering that load in a 2 3/4 inch shell.
