H1000 is a slow powder, but Retumbo is much slower yet, and as a generalization, the slower the powder, the more powder you must use to attain results. The more overbore the cartridge is, the slower the powder you should run. This is all generalizations, and theres exceptions to most rules, except safety. In the case of the 300 win, it doesnt need all that slow of powder to respond well. IMR4350 is what I load in the wife's 300win, and I am getting good results. My 7mm rem mag I am using retumbo, but I may start trying H1000. My 300RUM, I use retumbo in it, and it wants alot of it. Also lighter bullets usually like a faster powder then heavier bullets. H4831 is probably the slowest you need for that gun, and thats a step faster then H1000.