What year is your ruger m77 338 if the model is 79-51197?

That's the serial number, not the model number. The year of manufacture appears to be 1984. More details can be had by leaving a message including the model of rifle and serial number with Ruger customer service at 603-865-2442.With the serial number that you have supplied,79-51197 your Ruger model 77 rifle was made in the year 1985.