Stan,
You have so many people giving advice it must seem very complicated. This is your project, you should use the advice you are comfortable with and fits the equipment and components you have; if this is someone else's advice, my feelings won't be hurt. Different powders will work, you just have to adjust the charge weight required for the particular case being formed. I suggest you load a couple cases with 4 or 5 grains of powder and the grits, fire them and adjust the charge until you are satisfied or decide it is safer to anneal and fireform more than once rather than add more powder after noticing pressure signs.
With regard to reduced loads causing detonations, the reports were with slow burning rate powders, the classic case was with 4831 in the 270 Win. I have a 5.6X61R vom Hofe Super Express and did pretty extensive research trying to find a firsthand account of detonations (the .227" bullets I had required less velocity than the load data I had in order to shoot acceptable groups) but could not verify they actually occurred. I switched to a medium rather than slow burning powder, anyway. You don't need to worry about reduced charges of fast burning powders.
Mike
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