Go to the Remington Society of America and click the Manufactured link, it has the location and barrel codes for month/year of manufacture.
Serial 718943w
100-350 USD
They have date code stamps on the barrel which can be looked up on the manufacture date link on the Remington Society of America. --- Update: It's important to note that the barrel on the shotgun MAY not be the barrel that was originally on the shotgun at purchase. Check the serial number with Remington.
See related link.
http://remingtonsociety.com/rsa/questions/barrelcodes
The barrel date code is the primary method of dating a Remington. Of course, if the barrel is not the original barrel for the gun that complicates things. The Remington factory could probably date it by serial number. sales@countrygunsmith.net
Contact Remington Customer Service thru their website.
Made by the Remigton Firearms Company.
The W ahead of the serial number indicates that your Remington 870 wingmaster was made in 1972.
It's date stamped see related links for info.
Check this table for the answer: http://www.remingtonsociety.com/rsa/questions/barrelcodes