Yep... such a massively incomplete burn, that the granules remain.
I encountered the same problem with Lil' Gun in a small cartridge, a few years ago. Except, the Lil' Gun granules were fusing together, into a single mass. I just had to touch the mass to get it to break loose from the case wall, and the single chunk would fall out of the case.
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."