Contact Remington Customer Service thru their website.
Made by the Remigton Firearms Company.
Serial 718943w
The W ahead of the serial number indicates that your Remington 870 wingmaster was made in 1972.
They are all still made in Illion, New York, I believe.
100-350 USD
Do a search on barrel codes, I believe that will give you an answer
$2
Check this table for the answer: http://www.remingtonsociety.com/rsa/questions/barrelcodes
The 870 Wingmaster is still made in .410
It's date stamped see related links for info.
Depending on condition, the 870 Express is about $450, the 870 Wingmaster is about $725.
Remington Society barrel code lookup: http://remingtonsociety.com/rsa/questions/barrelcodes