The number that you listed for your Western Field shotgun is the serial number,not the model number.We would need the model number to give you some idea of the age of your shotgun.
Need more info. Which guage? 12 or 16? It looks like your serial number is missing a letter and/or a letter/number preceding or above the 40107. This information is needed to determine the year of manufacture. Please re-check and ask the question again. Thank you.