I weigh my brass, but contrary to Ganderite (who is a very experienced shooter) I seperate them into lots based on 1% of wt. If you are shooting .308 then 0.1gn increments are ~1% of wt, but if you shoot a .223 or WSM then the lots will be much different if you use an 'obligate' measure such as 0.1 gn, instead of sorting by a % of total wt.
I know many guys on here say you must measure volume, but I do not see the point, if the brass is thicker and has a smaller volume then it is usually heavier. I shoot F-class and do not know a single shooter either nationally or internationally who measures internal volume. I generally sort 1000 or more pieces of brass for a season, there is no way I am going to fill each one and measure the volume. It may be that some benchrest guys do this, but that is a different game.