At the time your gun was made, our North American Ammunition Companies were offering 28-gauge shells 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 longer shell of 2 7/8 inch with 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 also offered.
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
FIELD 28-ga 1 3-4, 5-8 ounce.jpg
Early Long 28-gauge Peters TARGET.jpg
FIELD 28-gauge, 2 dram, 5-8 ounce.jpg
With Parker Bros. policy of holding chambers about 1/8 inch shorter than the intended shell, a 2 3/4 inch chamber would be about right for the 2 7/8 inch shell.
The progressive burning powder, high velocity, 28-gauge load with 3/4 ounce of shot was introduced in a 2 7/8 inch shell in the 1931-32 time frame.
28-gauge Super-X #6.jpg
The 2 3/4 inch 28-gauge shell first appears as Skeet loads, just before WW-II. Shortly after the War the 28-gauge was standardized at 2 3/4 inch.
Whether your gun was rechambered to 2 3/4 inch at some time or came from Parker Bros. with longer chambers may be impossible to prove.