The term “grain” when discussing ammunition refers to a unit of weight, specifically 1/7000th of a pound. It quantifies the mass of the projectile, which is a crucial factor in determining its energy, velocity, and trajectory. For instance, a 115-grain 9mm bullet signifies that the projectile weighs 115/7000ths of a pound. This measurement provides a standardized method for comparing the weight, and therefore the potential performance, of different rounds.
The projectile’s weight significantly influences its ballistic performance. Heavier projectiles, measured in grains, tend to retain more momentum and penetrate deeper, whereas lighter projectiles usually exhibit higher velocities. The relationship between projectile weight and other factors like bullet design, powder charge, and barrel length directly affects the recoil felt by the shooter and the energy delivered to the target. Historically, grain weight has been a primary specification considered in ammunition selection, directly impacting choices made for hunting, self-defense, and target shooting.