The Ruger website, under customer service, historical data, rifle, M77, will have the serial number ranges for each year of production.
Ruger's website has extensive sn data.
1990
Ruger has extensive sn data for their products on their website.
Around 1981
If the Ruger website will work for you, it has sn data published on line.
Ruger's website has sn data.
1989. Data is on Ruger website, under Customer Service
IF the Ruger website is up, look under customer service
Go to the Ruger website. Under Customer Service, Historical Data, Rifles, M77, and the serial number groups for each year are posted there.
20 years old
Ruger has sn data on their web site. You can also call them.
contact the Ruger company directly with your question at http://www.ruger-firearms.com/