I own quite a few Ruger M77 rifles, rings by Ruger either come in 1" or 30mm, not sure what your "25M" is referring to.
There are a number of different set ups depending on which model you have, a standard M77 MKII will take a #4 ring (med) on the front and a #5 (high) on the rear mounting point, the photo from foxshooter69 shows these different height rings in stainless finish. The medium height front off set ring will give you what you are looking for assuming your rifle is a standard model and not a Ruger No1 model. If you want the standard blue finish I believe the front offset ring is a "4BO".