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Black powder has a low energy density compared to modern "smokeless" powders, and thus to achieve high energy loadings, large amounts of black powder are needed with heavy projectiles. The unit of measurement called "grain" dates back to medieval Europe. The average mass of a single grain of wheat was the standard for the grain unit of mass. The term "troy grain" was based on the average mass of a single grain of barley. The grain is used to measure the mass of bullets, gunpowder, smokeless powder, and preformed gold foil; it is the measure used by the balances used in handloading; bullets are measured in increments of one grain, gunpowder in increments of 0.1 grains.Black powder has a low energy density compared to modern "smokeless" powders, and thus to achieve high energy loadings, large amounts of black powder are needed with heavy projectiles.