What year is my Stevens 311H?

I just bought a Stevens 311H double barrel shotgun. I was wondering about how old it was? I think it is made after 1970 because it doesn't have the circled letter to date it. The serial number is D147299 Stevens Model 311H Series H. Savage arms Westfield, Mass USA. The gun looks new and I think it is an 1980's model gun. I would appreciate knowing the exact year is was made.
Thanks,