Dram equivalents were originally developed in the early 20th century to allow sportsmen an easy method of comparing the "new" smokeless powder loads to the then more familiar black powder loads. In effect, a shotshell with a 2-1/2 dram equivalent rating would be equal in velocity to a shell loaded with 2-1/2 drams of black powder--making the assumption that both shells contain the same amount of shot. Overall, the most important thing to remember is that the higher the dram equivalent, the higher the velocity for a given shot weight and, as a result, the more powerful the charge. There are no real dram equivalents for loads that didn't or couldn't exist in the black powder era. Key examples of these are steel loads and some of the heavy magnum turkey loads.
WARNING: Dram equivalents values have no relationship to the actual powder charge in a shell! These values should never be used in determining smokeless powder charge weights!