Weighing water from a case won't be too accurate in determining how much capacity the case has. Depending on how much out of round the case is, it'll have different amounts of room inside for the water.
Just weigh cases. For every 10 grains difference in weight, adjust the powder charge 1 grain. Heavier cases need less powder, and so on...... So you'll probably use 43 grains of 4064 under 168's.
I don't understand why one would not use commercial brass when military match brass isn't all that good. It was probably originally fired in service rifles and they all have out of square case heads. Military teams tried reloading that brass but gave up; it never shot as accurate as new, virgin brass. I've fired thousands of rounds of military match brass and never picked up one to reload. Match brass was not made for reloading; too hard and not all that great in dimensional quality.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master