This must be a common problem for Ruger. I had a #1 .416 Rigby with a similar issue. I wanted a custom quarter rib so that I could keep the scope's ocular ahead of the falling block. The quarter rib was completed and inletted for QD Talley's, and when the smith unscrewed the factory quarter rib he discovered it had some "preload" on the screws. My situation was not so bad as yours however, in that I was able to zero the windage of the factory sight.