WT, in the .300 Win. Mag., I would not use any powder slower than IMR 4350, and even this is a bit on the fast side!! My preferences would be: H4831, Alliant Re 22, Re 25, IMR 7828, H 1000, AA 3100, or Norma MRP. I have not tried Re 25, it is a recent arrival on the market. I have had great results with Norma MRP!! (But MRP is very similar to Re 22.) I just looked at my Speer Manual No. 13 (copyright 1998). It doesn't even show ANY loads using IMR 4064 or 3031 for any bullets of 150 grains or heavier in the .300 Win. Mag. (These two powders are NOT really suitable for any .30-cal. cartridge with a case capacity larger than a .30/'06, and even in the '06, there are better choices, also slower!!).

Keep yore powder dry!!