By middle screw I’m guessing you mean the front trigger guard screw. My experience has shown me the front trigger guard screw doesn’t factor into the accuracy of the rifle, tighten it up just enough to hold it in place. The angled action screw needs to be at 90 to 95” pounds, (not foot pounds).
The rear trigger guard screw is the difference maker though, you can toss out Ruger’s spec on that. I have four M77’s and none are set the same and they are all sub MOA rifles. I generally start with the screw loose, shoot a three shot group, tighten the screw and repeat. I’ll do this until I get my groups as tight as I can get them. I call it “torque tuning “, it’s worked for me.