I was in the ammunition business from 1989 to 1992. As a manufacturer, we were working closely with a French powder manufacturer named SNPE and purchasing powders by tons each year to load from .25 ACP to .50 Browning. Flakes, spherical, compressed spherical, tubular, multiple tubular, coated or not coated.
In no way graphite was INSIDE the powder.
graphite was a slight coating added (or not) at the end of the process, which purpose was to help the powder to flow in the various tubing bringing the powder from the explosion area to the loading shop and the loading machine and inside the machine to the currently filling cases.
We could order powder with or without coating, depending on loading machine type / throughtput. Graphite was almost ZERO regarding powder density at that time, and I doubt about the relationship in between graphite and powder density.
Anyway, I am having no doubt about graphite and load density achieved in using long drop tubes AND graphited powders.
A powder manufacturer trick is to mix non conformant powder batches (according they are same elements in composition and same structure) to achieve conformant burning performance regarding a particular powder label. That practice can lead to various aspect inside the bottle, more or less dark graphite coating or even coated / non coated granules.
Hope it helps.