Sporting powder grains are nearly spherical like well worn river rocks. Blasting powder grains have very rough shapes like freshly crushed stone. Due to the uniformity of size and relatively smooth grain shapes, sporting BP lends itself to fairly accurate measurement by volume. Blasting powder must be weighed if accurate quantity measurement is required. The graphite coating on sporting BP is quite porous.
Water vapor can penetrate the graphite coating.
Thanks to Bill Nelson for providing most of this data.