Roy, I think you have it by now. But here it is in my manner of thinking.
If it is real BP you can use weight. Since that’s about all I use I just weigh it on a scale to get my powder measure at the right setting.
Otherwise, for any substitute you use the equivalent volume, i.e. 60 gr by volume.
60 gr of real BP is what the volume device is calibrated to represent at the 60 gr volume mark. I never weigh a substitute (except just for curiosity).