according to Homer Prowley here is the method for finding case capacity with water but first you need to know some abreviations.
ratio of charge to bullet weight (RCBW), sectional density (SD), ballistics co-efficiant (BC), case capacity (CC), expantion ratio this is the ration of expanding gas in your barrel not how much your bullet expands on impact, (ER)
1. useing brass from the same company, and if possible lot number once fired in YOUR rifle
2. neck size only, then clean, then trim to length
3. weigh them empty, (you need 10 pieces of the same length and weight)
4. now weigh your 10 bullets (be sure they are the same weight)
5. useing the bullet you intend to use, with a q tip lightly lube the inside of the case mouth and with NO primerand no powder place the bullet in the case and chamber it in your rifle. As the bullet hits the rifleing it will seat it to the required length
6. weigh these 10 dummy rnds and add the total weight, divide that by 10 and you have your average (if your brass is the same length and weight and your bullets are the same weight then your 10 dummies should all be the same weight)
7. useing a hypodermic needle fill the dummies with water through the flash hole useing q tips to dry out the primer pockets
8. now weigh them again add the 10 then divide by 10 to get the average weight, (because of air bubbles there may be a slight differance)
9. subtract the " average of the "wet" from the average of the "dry" and you have your case capacity of water FOR THIS RIFLE AND BULLET COMBO ONLY
From this figure of "CC" and from the distance of the base of the bullet from the above "dummy" to the muzzle you can work out "ER", knowing your "BC" and "SD" numbers plus your true barrel length and "CC" together you can now use a slide rule to determine your powder, charge, "RCBW", velosity, chamber preasure and bullet drop.
SO, when you have at hand reams of confermed PUBLISHED reloading data why would you bother?