I checked the serial number on the Research Letter and the PGCA has no information for a letter.
Bill is right on. Here is a box from 1931--
Arrow Express Lacquered 3-inch 20-gauge 1931 vintage.jpg
I have or have access to all the Remington ammo catalogs through that era and nothing heavier then the 2 3/4 dram equiv. pushing one ounce of shot was offered in20-gauge, but I guess if someone ordered enough of them Remington would load them!?!
Serial number 153333 would be a 1910 gun, well before the above box, when loads like these were the factory offerings in 3-inch 20-gauge --
20-gauge 3-inch IDEAL.jpg
Premier 20-gauge 3-inch.jpg
Threaded Mode