Starting in 1921, Remington rifles are dated by a 2 or 3 LETTER code stamped on the left side of the barrel, about a half inch from the receiver. Not by the serial number. Search for Remington Collector's Association Date Codes, and you will find the table to decipher the letters for month and year of manufacture. They are small- a magnifier and bright light will help
1920
That is not a serial no of a Remington 1911A1 they stopped in 1945 with 2465139.
I checked www.oldguns.net and they show the manufacture date of Remington 1903A3 serial no. 3851292 as 1942.
RW isn't part of the serial no, it stands for Remington Works 1915
1912
1920
1924
1923
1912
1912
1917
1919