I have a .416 Taylor, Jim, on a custom Oberndorf Mauser. I have used RL15 as my go-to powder mostly, up to 75gr. with a 400gr. Hornady. I haven't chronographed that load in my rifle but Chuck Hawks data suggests 2394fps with that load. Even though my rifle weighs just over 9lb., I find that 75gr. results in more recoil than I like so I reduced my load to 71gr. with the 400gr. bullet. I have also used 75gr. IMR4895 with the 350gr. Speer, I think that's the bullet to work with. My rifle does not like the Barnes 300gr TSX with any powder or load, which is disappointing.