There are plenty of conversion charts available to learn these quaint bits of trivia. But, 27.34 grains is the accurate amount, by WEIGHT. since BP is measure BY VOLUME, we tend to round things off, and up a bit. ERGO, 27.5 grains will get you there.
There are 7000 grains to a pound; 437.5 grains to an ounce. 2 drams = 55 grains( roughly). 4 drams equals 110 grains( 2 x 55= 110).
Actually, now that you know what a "Dram" of black Powder weighs, you have a better chance of understanding why modern shotgun cartridges list the Dram Equivalent Load on the outside of the box, along with the weight of the shot in ounces, and fractions of an ounce.
If you then, also, Understand the Rule of "17", which tells you the diameter of the shot pellets in bird shot,you can best understand what kind of load(s)to put in a shotgun. ( Subtract the # of the shot from 17, and the result is the diameter of pellet in hundredths of an inch. So, for example, # 6 shot is .11" in diameter; # 2 shot is .15" in diameter; and # 8 shot is .09" in diameter.)