rcpigg65;
Good evening to you sir, I trust the weekend treated you well and you're ready for the upcoming week.

Here's a link to Ruger M77 serial numbers which should narrow the manufacture date down.

http://www.ruger.com/service/productHistory/RI-M77.html

While some of the barrels back then did prove to be a bit more picky about which bullet they liked than those we have today, usually back then we were able to find at least one bullet that worked well with them.

Hopefully that was useful information to you sir, good luck with your new rifle and all the best to you for the remainder of the summer.

Dwayne

The most important stuff in life isn't "stuff"