I have to do a bit of research to find out the year of introduction. For a German rifle made post-1940 you don't need the serial number for dating, as the date, month and year, is part of the proofmarks. The proof date may be coded at the request of the maker. If coded, the letters A -K (J is not used) stand for the digits 0 - 9. So June 1990 may either be marked as 6.90 or 6KA or GKA.