I'm thinking the accuracy would probably get worse as the charge of loose powder goes up, because it appears the variations in velocity get bigger. And the burning efficiency gets worse. But you never really know about these things until you try them.

I have also been wondering about using a stack of 30 grain pellets. One of the contributors to this board recently suggested that there was an advantage to having more pellets at the same charge weight. Might be an interesting experiment . . . .