The "standard" 28-gauge shell was a 2 1/2-inch shell with 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 pushing the same 5/8 ounce of shot was put up in a 2 7/8-inch shell.
28-gauge Bulk Smokeless Powder Loads 1915-16.jpeg
28-gauge Dense Smokeless Powder Loads 1915-16 Infallible or Ballistite.jpg
NITRO CLUB 28-ga 1 3-4 dram, 5-8 ounce.jpg
NITRO CLUB 28-Gauge 2 7-8 inch #7 1-2.jpg
In his 1910 book, Chas. Askins writes of hand loading 2 1/8 drams of bulk smokeless powder and 3/4 ounce of shot in the 2 7/8-inch hull for his 6 3/4 pound, 30-inch barrels, Parker Bros. 28-gauge. My 1915 vintage Ithaca Flues No. 1 Special 28-gauge with 30-inch barrels has 2 7/8-inch chambers. Whether it left Ithaca with them or was lengthened later who knows.
Our North American ammunition companies finally got around to applying progressive burning smokeless powder to the 28-gauge in 1931/2 when the 3/4-ounce high velocity loads came out put up in the 2 7/8-inch case.
Super-X 28-gauge #6.jpg
HIGH VELOCITY 28-gauge #6.jpg
NITRO EXPRESS 28-gauge #7 1-2.jpg
The only Flues era Ithaca Gun Co. catalog I have that gives chamber lengths is the last one in 1925, and it states 2 1/2-inch for the 28-gauge. With the introduction of the NID in 1926, Ithaca added the .410-bore to the offerings and dropped the 28-gauge though they did continue to make some. The 28-gauge returned to the Ithaca Gun Co. catalogs in the first 1932 catalog. From the April 1932 issue of
Field & Stream --
NID 28-ga Field & Stream April 1932.jpg
Just before we got into WW-II, our ammunition companies began offering 28-gauge 3/4-ounce Skeet Loads put up in a 2 3/4-inch shell.
Xpert 28-gauge, SKEET LOAD, 2 3-4 inch, 3, Aug 2019.jpg
The regular 28-gaauge Skeet Load had been the "standard" 2 1/2-inch load --
Xpert 28-gauge, Skeet Red Dot load.jpg
By 1950 our North American ammunition companies standardized the 28-gauge in a 2 3/4-inch shell.