Reloading .303 British : Cast bullets

I found this.  It gives two bullet weights but uses the same charge weight for both bullets using, for the most part, "H4895, BL-C(2), H380" Medium burn powders. If you use Hodgdons mathematical formula using the H4895 max charge of 34.0 x .6 = 20.4 starting grains. The Hodgdon reloading manual #26 gives a max charge weight of 38.0 grns of H4895 using a 180grn Sierra SP. It would be expected then that, a safe charge weight scale, within a reasonable margin for a cast bullet of the same weight to be between 20.4grns starting and 24.4grns max charge weight. IMR4064 has a starting weight of 37.0 ,exactly  the same as Varget using the Sierra 180grn SP. If you use the formula 37.0 x .6 = 22.2grns starting weight, you have a working load using a cast bullet. Not exceeding 25.5grns, just to be safe of excessive lead fouling while still producing sufficient velocities... Sidenote: I added the IMR powders because they have identical burn rates including  the Varget.