Small unit of weight that is traditionally used in the measurement of the powder charge and bullet weight in ammunition.

1 gram(g) == 15.43 grains(gr)

For example, in the cartridge .30-30, you use a .30 caliber bullet over a charge of 30 grains of black powder. The bullet weight can and does vary depending on the intended application.

Also note that it requires much less smokeless powder to create similar velocities to that of a certain charge of black powder. As always, consult a reloading manual to be safe.