During the years the Ithaca Flues Model was produced in 28-gauge, 28-gauge shells were offered by our North American ammunition companies in two lengths. The "standard" shell was 2 1/2 inch and carried a load of 1 3/4 drams of bulk smokeless powder or 14 grains of dense smokeless powder such as Infallible or Ballistite pushing 5/8 ounce of shot.
A slightly hotter load of 2 drams of bulk smokeless powder or 16 grains of dense smokeless powder such as Infallible or Ballistite pushing the same 5/8 ounce of shot was put up in a 2 7/8 inch shell.
The progressive burning smokeless powder, high velocity, 28-gauge load with 3/4 ounce of shot wasn't introduced until 1932, well into the NID era, put up in the 2 7/8 inch hull.
Just before WW-II our ammunition companies began offering 28-gauge Skeet Loads in a 2 3/4 inch case.
The hunting loads remained in the 2 7/8 inch case for a few years after the war, just into the pie crimp era --
Then the ammo companies began putting all their 28-gauge loads in the 2 3/4 inch case --