Black powder

If I make some BP using air flote charcoal [ball milling 4 hr.] the
stuff turns out nice and black. I didn't like the mess with loading
and weighting out the air flote so I used 80 mesh charcoal. After 4
hr. in the mill, it turned out a gray color. I'm at a lost as why this
is happened. I would think that ball milling would turn the 80 mesh
into air flote and it would end up the same as using air flote in the
first place.
.