E, you're on the right track. The Berger 215 Hybrid or the 230 OTM with H1000 or Retumbo, Federal 215M primer and WBY brass with the 230 taking full advantage of the 30/378 large powder capacity. My 30/378 shot best with Retumbo, but a friend's was more accurate with H1000. Usually no two rifles will realize maximum accuracy with the same load. Start low and work up with powder charge and play with seating depth after a powder is found to be most accurate. With the freebore Weatherby has your bullet will nearly fall out of the case before touching the lands. Try just under magazine length to start, or the Berger suggested COAL. My best load was a bit under max with great accuracy and the elk don't notice a little less velocity. Good luck