Recently rebarreled my Savage 300win mag to 338 win mag. I have been working up loads for heavier bullets, 225, 250, 265 300 grn accubond, LR accubond bullets & RDL nosler bullets, are the powders tried that appear to be working well are. H4831, IMR4831, H4350, IMR4350. I have some RL19 but haven't tried it yet, and am going to try H1000 and IMR7828. But will probably settle on one of the first four mentioned as had some very good grouping several 3 shot groups were touching and had reproducible velocities, but just breaking the barrel in less than 60 rounds into it. Pulled the starting info off of the Nosler website been a lot of fun, really like the caliber. The 300 grn don't appear as stout as some of the 300 win mag rounds was shooting my 300 win mag BAR during the same range session.