I guess my point was that whether the modern measure or a BP measure it's still volume.
Changing the volume of the modern measure to achieve a constant weight is just that - changing the volume. A 100gr charge becomes a 97 or 103gr (just a guess) charge when you're trying to repeat the weight of the previous load.
My question is whether the volumetric charge is constant or the weighed charge is constant as far as actual results. Velocity would give a comparison.