Every rifle will be different. One might like Retumbo and another H1000 or something else They may like different bullets also. I am trying 5 different combinations of powder and bullets to see which my rifles like's best. With a cartridge like the 300 RUM, you really are better off with going with a heavier bullet unless your rifle like's the 180's best. For lighter bullets, faster powders like H1000 are sometimes a better choice (more efficient) than Retumbo. Retumbo is a slow buring powder more suited for longer barrels and heavier bullets. Something to think about.
-MR