All black powder and black powder replacements should be measured by volume, if you want to weigh the charges measure out the volume you want then weigh that. You will find that the actual weight is less than what a volume measure says it is but that is how it is.
The Shockey gold is a replica black powder and is designed to measure by volume just like Black powder. So 100 grains of JSG by volume would be the equivalent of 100 grains by volume of black powder. The only exception to that would be Hogdon's Triple 7, it is more powerful than black powder, Hodgdon says to reduce by 10% to 15% by volume to duplicate black powder loads.
Of interest the current American Rifleman magazine has a very good article that compares most of the currently available black powders and replicas. Gives velocities, compares, accuracy, ease of cleaning, etc.