Mark,
I spray all my powder so I use the smaller .008 size. I can use the .015, but usually don't. Brown Is one of the worst colors to ad glitter to. I cut it 4 to one with clear and add lots of glitter. The brown becomes semi-transparent and a little lighter, but the glitter shows up better. I can add another coat to make it darker and the glitter still stands out because it is being re-applied with the new coat.