How did Thomas J. Rodman change the shape of black-powder grains?

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coal miner loading a drill hole with an explosive — explosive A coal miner loading a drill hole with a water gel explosive called Tovex.

Thomas J. Rodman did not merely change the size of black-powder grains; he invented prismatic and perforated-cake gunpowder.1

By shaping the powder into these specific geometric forms, Rodman ensured that the propellant burned evenly. This design allowed for the controlled expansion of gases within a cannon, preventing the sudden, intense pressure spikes that could otherwise cause a barrel to burst. This innovation was a significant advancement in internal ballistics, as the burning rate of black powder is a surface phenomenon—larger, specifically shaped grains expose less surface area to combustion, thereby slowing the rate at which propellant gases are produced compared to finer, traditional granulations.123