Net research. From an enthusiast web board. The serial # falls in the 20 million range. That plus the arsenal stamp ( characters in a triangle ) equals manufacture of 1975 according to a chart put up there.
CC
arsenal 26? mine was built in 1963
this is the absolute best site i have found for S/N research
http://chinesesks.weebly.com/dating-the-chinese-sks.html