Using the table provided by 243winxb, THANKS and using some arithmetic and assumptions, I calculated that this particular shotgun was made in April 1971.
By dividing the total production of 5 years by 5 years, I get an number made per year. (31,209) Then, when I get the number range for the year, I divide by 12 months, and get 2,601 made per month.
My assumptions are that an equal number of guns were made each year, and each month.
Unable to figure in factory closings for holidays, etc. so it’s still a bit of a guess, but a calculated one.