I thought the idea of sorting brass by weight has been proven to mean nothing or was it weight has nothing to do with volume?
Not "nothing" but not "absolutes", either.
Consider this, since the brass is the same size on the outside, and capacity is determined by the size of the inside, the heavier case must have either thicker walls (more brass) OR it has the same thickness walls made up of a heavier alloy.
SO, the heavier brass MAY have less capacity, OR it may have the same capacity and be made of a more dense alloy.
There is a relationship, but its not an automatic one where every batch of cases from every maker can be plugged into a general formula and have accurate results.
I think this is one of those things where formula can predict general trends but actual differences (amounts) must be determined by weighing and measuring the cases you are working with.
Or not bothering to worry about it, and just working up your loads with what you have, specific to what you have.
for example, GI brass is usually heavier than some/most commercial brass, but you can't tell exactly how much of a difference that is going to make only that there will be a difference, the exact amount of which requires measuring what you have.