A "dram" is a unit of measure used in the Avoisdupois weight system of pounds, ounces, etc. It was used to measure black powder charges for shotgun shells. Therefore, the larger the drams, the more powerful the shell. With the transition to smokeless powder, the power (velocity) of a shotgun shell was expressed as "drams equivalent" since it was not practical to express the weight of the smokeless powder which is much less bulky than the old smokeless powder.

An example would be a 3 dram equivalent 12 gauge shell. It contains the amount of smokeless powder needed to give the velocity of a 3 dram charge of black powder.