They are date code stamped on the barrel on left side in front of receiver. A barrel location diagram and the date code table (month/year) is available on the Remington Society of America.
Serial numbers by year for the 870 Remington Model.
1920
Manufactured in 1913.
Need the serial number to answer.
Look at the manufactured date link on the Remington Society of America for details.
Check the manufactured date link on the Remington Society of America for details.
Go to the Remington Society of America and click the Manufactured link, it has the location and barrel codes for month/year of manufacture.
12 guage? 1908
First year 1909
Check the date code stamped on the barrel, details on the Remington Society of America manufactured date link.
Check the manufactured date link on the Remington Society of America for details.
Check the barrel date code, details on the Remington Society of America, Manufactured Date link.