If you provide the serial number (on the butt of the frame), someone can look up the date.
Hope this helps.
Steve
1977...
The Standard Catalog of Smith and Wesson states that 1977 was the year for serial numbers 10K0001 - 24K9999.
Additionally, yours should be a 15-4, as the dash 4s were introduced in 1977, according to the above reference work.
Hope that helps...