The "Drams Equivalent" business came about as the various dense smokeless powders began coming into use in the late 1800s and early 1900s. Prior to that both black powder and bulk smokeless powder (E.C., Schultze, DuPont, etc.) were measured by dram (volume), as black powder had been in earlier times to pour down the mouth of your muzzle loader. Shooters of the day had a warm fuzzy feeling for how their favorite load of 3 1/4 drams of powder and 1 1/4 ounces of shot (or whatever) performed. Then along comes dense smokeless powders such as Laflin & Rand's Infallible, Nobel's Ballistite and Walsrode, which are loaded by grains (weight). Joe Nimrod goes to the gun store and sees boxes of UMC Nitro Clubs loaded with 24 grains of Infallible and 1 1/4 ounces of shot, and he doesn't have that warm fuzzy feeling of how that load performs. So, the manufacturers came up with Dram Equiv. to put on their shell box which means this shell is loaded with enough dense (or after the early 1920s progressive burning) smokeless powder to give the same velocity as a 3 1/4 Dram load of black or bulk smokeless powder and thereby to give Joe Nimrod his warm fuzzy feeling and product loyalty. This this Drams Equiv. business should have gone away with WW-I and the companies should have began just putting the velocity on the box, but shooters are a hidebound lot!!
Just because you pick up some low brass shells at Wally World and they are listed as 2 3/4 drams equiv. and 1 1/8 ounces of shot (or any other load), doesn't mean they are any lower pressure then a 1 7/8 ounce 3-inch Magnum load. To produce lower priced shells the manufacturers use a lesser amount of hotter powders to give the desired velocity at a cheaper price. All they have to do is stay below the SAAMI spec. which for 2 3/4 and 3-inch 12-gauge shells is 11500 psi.
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