The dating by serial number isn't an exact science with Ruger. Many times they have models sit or forgotten and not ship until long after they were produced. Some have sat for years. Here's also just WAY to many incidents of a particualr specimin having an odd part or two left over from a previous run. Best bet, call Ruger and ask for the records division. Request from them a shipping data write up on your gun. Can't recall if it's a fee service now or not, but even so, it'll possibly prove something unique if there is, about your particular rifle.