Rifle cases water capacity? Why?

[Unclenick]

It really depends on the brass. As Houdawg says, if you are trying to match to a tenth of a grain, you are wasting your time. But some brass varies a lot. .300 Win Mag brass with as little as 87.5-grain water overflow capacity can be had (Tula) and brass with as much as 95.5 grains of water overflow capacity can be had (Norma). It's enough that QuickLOAD's author made the different brands of 300 Win Mag brass different cartridges in the database. A nearly 9% spread in capacity is too much to ignore if you want to be hitting a target 1000 yards away.

.308 is more uniform in volume now than it used to be. So is .30-06. A 1981 NRA book I have mentions a .30-06 Peters case that weighed 215 grains. LC is usually 95-ish

Here's a chart made up from some WW .308 Win brass I bought bulk at Camp Perry one year. There are a few that were off the edge of the chart, with the lightest being 153.5 grains and heaviest 159.5 grains. I also measured these for neck wall runout and found one with a whopping 0.008" TIR, but the second worst was half that bad and most averaged around 0.002". You can see four distinct bell curves, each representing distribution around an average for a particular set of tooling, so I don't expect uniformity here.

Here is a much smaller sample of Lapua .308 brass. You see it is much tighter and it is unlikely a load adjustment would be needed.

 

[F. Guffey]

And then there was the shooter/reloader/writer of everything gun related. He purchased 500 cases from one manufacturer from what he believed to be 'one lot'. He sorted and separated, shot and sorted and separated again until he settle on 43 cases that were perfect.

He then started over sorting and separating and matching the culls. With some of his culls he shot one hole groups by indexing the cases in the chamber. All of this happened over 47 years ago.

F. Guffey

 

[jamaica]

"I get the point of using water capacity to measure cases volumetric capacity but, my question is when should the practice be applied?"

This onery ol man is gonna say: Forget it! Shine em up, load em up and go shoot em. Have fun! But then I have only been reloading for 63 years, what do I know?