Fwiw.... I have one of the early 300 Weatherby ultralight and it was made by saco defense for weatherby when they first came back to United States. I think I half wore out the barrel trying to find a good load for that gun.... and it shot almost every bullet and powder combo poorly. Then I started seating the bullets very deep into the case and I couldn't believe how the gun came back around....it's now moa and under.
If I had one recommendation for the original poster I would say try different seating Depth's, especially those quite deep. I've never seen such a swing in accuracy for doing that in my life.
