I have loaded for the 7mm/300 Weatherby for the last 25 years or so. My go-to powder has been IMR7828 with the 162-grain Hornady BT Interlock. The rifle belongs to a younger brother who I load for. My suggestion is to use 7MM STW load data as a starting place. I advise caution because the chamber and throating are all over the place. I know that the smith who chambered my brother's rifle used what amounts to free bore.
