Years ago I built a .338/08 on a model 77 and took it to Africa for plains game. The cartridge was excellent for this use. It was very accurate also.
The gun itself was a problem. Perhaps not gun but twice I short stroked and was not able to make a quick follow up shot. (Un-necessary follow-ups. But that is another story) Yes short stroke is a shooter error. I sold the gun shortly after I came home.
4 years after I made that hunt, Federal came out with the Commercial version .338 Federal.
This is a good cartridge, a very good cartridge.
Loose Ruger factory rings, in 40 years of gunsmithing full time, part time and some times, this is a common problem. The mount screws are soft and stretch. The dove tail nuts are soft also. I believe it was Millett that sold replacement screws and that solved that problem in the past.
I recently scoped my Ruger No. 1 450/400 3" NE using Ruger extended rings. The screws in the rings seem strong and have not deformed. If they were soft I would think issues would have popped by now. 3 years, one white tail, one hog and one bear later, no problems.
Loose Ruger rings , replace the screws if you can or get some one else Ruger rings and problem solved.