Weird cleaning issue with my 91/30

[EBR Works]

Where can I find a "key" for what the marks mean?

You'll find them here along with all the info you'll ever need:

http://www.7.62x54r.net/

[alks207]

Rover, it sounds like you've got a really accurate 91/30, which sometimes can be hard to find among the recent re-furbs. At least all of the 91/30's I have don't shoot very accuratelly. However, re-finishing the stock and re-bluing the rifle will not improve your accuracy. PLEASE leave the rifle as is, no matter how bad you think it looks. More importantly, post some pictures of the rifle.