Stat, I think you'll do better with some load data from something like the Lyman Cast Bullet Manual. When you start backing down on the normal rifle powders, you start getting incomplete and even somewhat erratic burn with the powders. I've not had any terrible issues with this practice, however, what I have discovered is that it's really easier to work UP with a slow burning pistol powder or very fast burning rifle powder than it is to try to load DOWN with a slow burning rifle powder.

Let me know if you need me to look up some Lyman data for you with this method. I've got the books. 2400 is an EXCELLENT powder for this project!