Wolf killer,
I had exactly the same experience with a Weatherby Mark V in 7mm Weatherby Magnum. It was the poorest shooting rifle I ever owned. A good friend had the same experience with his 270 Weatherby Magnum (Mark V).
I tried all kinds of different combinations of bullets/powders/primers/ cases....to no avail. I finally got rid of it in frustration. For sheer accuracy, I'd rather have a Savage!

Clint