Powders are usually selected based on the burn rate. Burn rate is mainly controlled by 3 factors: chemical composition, grain size and grain shape. Chemical composition basically determines the energy density, sensitivity and relates to burn rate. The grain size is affects how the burn can propagate through the charge. The grain shape also affects the propagation of the burning of the charge. The grains usually come in cylindrical, spherical or flake powders. Grain shape can also have affects on metering. Powder is usually measured by volume, as it is an easy way to measure powder for a given charge. But usually spherical has the best metering ability as the grains tend to evenly flow. With flake powders the grains tend to stack up an jam, which causes poor ability to meter. Shown below is a table of powders listed by burn rates.
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