Correlation between brass weight and internal capacity?

[Teletiger7]

Just recently got into reloading rifle in .223 and .308 so wanted to see what opinion was on sorting brass according to weight. I currently dont do this for my "blasting" ammo, but seems like alot of people do this for when they want to shoot for accuracy(hopefully i'll get to the point where it would even matter). How accurate is it to assume that cases of same weight will have same internal capacity? Do you sort your brass by weight? What is your method, how close do the cases have to be?

[CSACANNONEER]

I know a couple of people who have measured case volume by decapping, reinserting the SPENT primer upside down and then measuring case capacity with water. They have also wieghed their brass and found that, although there is a little bit of difference, both meathods end up with close to the same conclusions.

[Teletiger7]

So does increased weight usually mean less internal capacity? I noticed that federal .308 brass is usually around 180 gr but some other brands I have seen as low as 160 gr.

[Beelzy]

Heavier cases don't always equate to less capacity, they could simply be
a tad thicker or longer.

I sort cases by maker lot (if possible), then maker, then measure, then by weight. I really only do the weigh in for rifle cartridges as I like to shoot long range. That's when weighing is of benefit.

[ar15barrels]

Heavier cases don't always equate to less capacity,
they could simply be a tad thicker or longer.

Thicker cases actually DO mean less capacity.
When the round is fired, the case blows out to fill the chamber so the outsides are the dimensions is the same no matter how thick the case walls are.
The thicker walls just leave less volume inside.

However, differences in alloy wll also contribute to differences in weight just as much as differnces in construction.

So, sort first by headstamp, then by weight and throw out the cases that are WAY out of the rest.
Make sure all the prep work is done the same before weighing.
If you have enough cases, seperate them into about 1gr intervals.
Otherwise, 2GR is not too much variation on a 308 case within a group.

There will be a few percent that are WAY heavier or WAY lighter.
Those are the cases that cause fliers.
Dump them.