A unit commonly used to specify the mass of a bullet. One pound is equal to 7000 grains. The powder charge of a bullet is also measured in grains, though it is the bullet mass that is listed on the box.

Actually, it is a measure of weight, not mass, the two of which are interrelated by Newton's Second Law of Motion. As we are in the English Engineering or British Gravitational system of units here, as opposed to the friendly SI, I'll go no further than that. Most of you probably don't have much engineering background, so I won't go into slugs and pounds mass or the horror that is gc, as it is quite evil.