Do a search on barrel codes, I believe that will give you an answer
See related link.
http://remingtonsociety.com/rsa/questions/barrelcodes
Check date code details link - Remington Society of America
From the date code stamped on the barrel. Look for the manufactured date link on the Remington Society of America for details.
Check the Remington Society of America, date barrel codes and location. http://remingtonsociety.com/rsa/questions/barrelcodes
Check this table for the answer: http://www.remingtonsociety.com/rsa/questions/barrelcodes
Go to the Remington Society of America and click the Manufactured link, it has the location and barrel codes for month/year of manufacture.
Check this table for the answer: http://www.remingtonsociety.com/rsa/questions/barrelcodes
In 1950 Remington introduced fifteen versions of the Model 870 shotgun, in 12, 16 and 20 gauges.
Look at the date code stamp on the barrel, see related link.
Remington Society barrel code lookup: http://remingtonsociety.com/rsa/questions/barrelcodes