I have to digress... fireballs do nothing for accuracy and simply highlight the fact that you have unburnt powder exiting the barrel.  While that may impress some kiddies, as Chuck said, it can temporarily dazzle (blind) the shooter, and serves no practical purpose.  I prefer to worry more about my accuracy (as I'm usually practicing for a match) and less about impressing others.

I use 40 grains of IMR-4350 with the 220 gr bullet for my Krag, and it's definitely the dirtiest of powders.  I've been shooting this tried and true load for more than a decade.  However, my plan over the winter is to develop a load with the 220 gr RN and H4895, which should burn cleaner, and more complete.  If my accuracy suffers (remember, not all Krags like the same food), then I'll go back to my tried and true load!