I have a Ruger 77 in 6mm Rem and it likes 70 GR bullets the best. The best bullet I have used is the Sierra 70 GR Blitzking.
I don’t punch paper that much with it, it’s mostly for ground hogs. I won’t get into charge or powders since it would be meaningless for your gun, but for my Ruger it likes them hot, but safe loads. 4895 works well.
Back in the 80’s when I purchased the gun I had the same problem, I just couldn’t get groups with it.
A suggestion from a great gunsmith, he measured the chamber in the gun and I length trim to the exact length of the chamber and seat the bullet so it just touches the throat. This gave the gun sub 1 MOA’s at 100 yards.