Supposedly the "Drams Equivalent" markings we still see on many shotshell boxes were based on using an amount of smokeless that would give a velocity equal to that amount of Black.

I wasn't around 125 years ago but some say that modern Black Powder is not the equal to what it was back then. Supposedly Black Powder peaked in its strength & effestiveness in the late 1800's & has gone in decline since.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra