Grain
A unit of weight used for bullets and powder; 437.5 grains equals one ounce.
Also: gr
Grain (abbreviated gr) is the small weight unit used in ammunition specs. A 9mm load might be 115 gr or 124 gr; a .308 load is typically 150–168 gr. Heavier bullets within a caliber generally have lower velocity but more momentum and recoil. Powder charges are also measured in grains.