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Why do finer grains of black powder burn faster than larger grains?
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A coal miner loading a drill hole with a water gel explosive called Tovex.
Because the burning of black powder is a surface phenomenon, the rate at which it burns is directly related to the amount of surface area exposed to ignition. Finer grains possess a greater total surface area relative to their volume compared to larger, coarser grains. Consequently, a fine granulation allows for more rapid combustion because more of the material is exposed to the flame simultaneously.12
In contrast, larger grains burn more slowly, which historically allowed for better control over the pressure generated within a gun barrel. By adjusting the size and shape of these grains, manufacturers can effectively regulate the burning rate to ensure safety and performance.1