Ruger rings work the best.
http://www.midwayusa.comOptics
Bases,mounts and adapters
Ruger
Ruger factory ringmounts
Just pick your finish, height and either 1'' or 30mm.
M77's use one ring lower than the other and are numbered 3-4-5-6.........
So as an example--you'll need a 3 and 4 or a 4 and a 5---and so on.