I've recorded guns well into the 240xxx range that still have the serial number in that location. The lowest I've recorded with the grade, gauge and chamber length there is in the mid 238xxx range with a Remington barrel date code of BJ B = January J = 1940. Is there a Remington barrel date code on the barrel flat? Here is the barrel date code on my 16-gauge VHE --
241968 01a 26-inch, 16-gauge, XJ X = December, J = 1940.jpg
The SAAMI meeting where it was suggested that manufacturers start marking the chamber length on their guns was in 1937. I have Remington pumps and autoloaders from 1938 that are not marked with the chamber length. I don't have a 1939 gun from Ilion, but those from 1940 are marked with the chamber length.