Guns and Ammo, August 2002 has an article entitled "More bang for your buch", and enclosed is a burn rate chart with densities of all listed powders. The author, Bob Forker, attributed the list to Lee.
Anyway, Blue dot is listed at 11.561 grains per cc, 800X as 9.337. For comparison, Unique, the old standby for reduced loads, is listed at 9.158 g/cc. About the bulkiest powder in that area of the chart is Herco, at 8.913. The bulkiest powder of all on the list is Clays at 6.840, followed by Red Dot at 7.077.
Hope this helps, I have always thought more information is better.