While longer than the "standard" 2 1/2 inch 20-gauge shells were around from virtually the beginning, just like longer 12- and 16-gauge shells, They didn't generally carry a heavier load, just more and better wadding for a better gas seal. By the early teens, the longer 20-gauge shells were being offered with loads of 2 1/2 drams equiv. and 7/8 ounce of shot as opposed to the max loads in the 2 1/2 inch shell of 2 1/4 drams equiv. and 7/8 ounce of shot. The famous "Widgeon Duck Club" heavy Parker Bros. 20-gauge guns were made for these 3-inch shells. Also, briefly before WW-I the J. Stevens Arms & Tool Co. offered their No. 200 pump gun for 3-inch 20-gauge shells --
I have a Parker Bros. GH-Grade heavy 12-gauge of 1889 vintage that was back to Meriden after WW-I for a set of 32-inch 20-gauge Vulcan Steel barrels with 3-inch chambers --
Here are some Rem-UMC Arrow long 20-gauge shells of the 1913-14 vintage -- 3-inch --
2 7/8 inch --
By the later 1920s, at least Peters Cartridge Co. was offering their progressive burning powder loaded High-Velocity shell in longer lengths --
and here is a box of their 3-inch shells with the 1 ounce High-Velocity load --
