I'm not sure when they were made, but I have a 351K which was a later model and it has no serial number. U.S. law required serial numbers on all firearms starting in 1968, so mine was made before that and yours is older than mine. As far as accuracy, mine is consistantly minute of pop-can accurate at 50yds and isn't fussy about what ammo you feed it. No jamming or feeding issues either.