Grain is a unit of measurement used to describe the weight of a piece of ammunition, specifically the weight of the cartridge projectile (the part that is propelled forward from the firearm) . One grain is equal to 1/7,000 of a pound or 1/437.5 of an ounce. The grain weight system is used to measure the mass of a piece of ammunition, and these measurements of mass help determine the correct size of ammo to use for specific shooting purposes. The weight of the bullet can affect factors such as accuracy, recoil, and terminal ballistics, and it is important to use the correct bullet grain when hunting or participating in precision shooting competitions. However, for activities like plinking and close-range shooting, the weight of the bullet does not have much of an effect on performance.