Thread: Case capacity question.

Hi, I am new to reloading and this forum and would like information on measuring case capacity. What is the best way to do it ? I have been told that brass of the same calibre is likely to have different volumes depending on the manufacturer. Is this true and if so how much effect will it have on the pressure generated ? If this has come up before I'd appreciate being directed to the thread. Thanks.

most fill the case with water, I think you then weigh the water. but I would imagine results would vary.
the better question to you is why...? as a new reloader, just get the same brass in a batch and use it, rather than different makes etc. it may seem like a good idea to use up old bits you have lying around but its really not.
if you have a load sorted and want to change batches of brass, start low and work up.
in the real world different brass would make a difference but not huge. but play safe and work up.

If you are looking to start reloading never mix brass from different manufacturers. That is really one of the 10 commandments of reloading. The best option is to buy the brass you will need in one purchase. If picking up range brass only use brass with the same head stamp. If you are interested in sorting your brass weight it. Good luck.

Yes different makes can have different volumes and it does have an effect on pressure and velocity but with a standard book load and a hunting rifle you won't pick any difference it's only when you start pushing for speed and absolute target accuracy especially at long range that it becomes evident.
The biggest issue is quality of brass varies. Some makes are excelent for reloading others are "scrap"

No doubt the forum autostuff has offered you this thread, where they discuss it but I don't think it quite answers your question.

Case capacity, measured in mL is used to compare different cartridges eg 308 vs 3006.
Within a batch from the same manufacturer, cases are often sorted by grain weight, to remove outliers and designate a set or two with very similar volumes. The best time to do this is before they are first fired because powder deposits build up weight and over time as you trim, chamfer and ream pockets each case needs a different treatment and the 5th firing weight won't reflect the amount of brass originally in the walls and base. I don't know why brass varies so much in how much needs to be trimmed after just a few firings.

Yes, differences in case volume will lead to differences in pressure. How much depends on the size of the cases, the amount of difference between them, the type and the amount of powder, and the chamber it's being fired in. Even knowing all the variables, you'd still need specialised pressure tracing equpiment to give you an exact answer on a case by case basis.

Just pick one headstamp to work with (for consistency's sake) then start low and work up. Your rifle won't care whether the type you used was thick, heavy, low volume stuff, so long as you developed the load accordingly, following safe practice.

Just weigh each case and cull the extream outliers light and heavy.

Thanks for all the advice, I appreciate it. I have some brass and just recently bought some from this site. Weigh it, batch it and work up following safe practice is now the plan.

As time and experience goes by (with corresponding less time to do stuff), you begin to realise that it makes little difference to minute of deer and become quite happy to just reload the lot.

Greetings Andygr,
I have made a bit of a study of .308 W case capacity. Cases on hand range from 155 grains for Super X (older Winchester) to 187 for GFL (Fiocchi I think) or 32 grains variance. Brass has a Relative Density of about 8.8 so about 3.6 grains of H2O or 3.3 grains of powder. This is huge. I have loaded some test rounds to check how much difference this amounts to in velocity but have not chronographed them yet. Based on earlier work with Federal cases (about in the middle of the range) I am expecting about 100 fps more velocity with the heavy case. This would be equivalent to adding 2 grains more powder in the lighter case. The extra velocity comes with extra pressure (about 5,000 psi for a rough estimate) and is likely to land higher on the target. With my original .308 in its wood stock would have printed about 50mm higher at 100 metres.
You are on the right track Andygr, with weight batching. This is what I do but still keep head stamps separate. I have measured case capacity in the past using ball powder which is less messy than water then converted it to cc's using the powder density. I think I will just weigh the cases in future.
Regards and all the best Grandpamac.

I've been reloading for a while, I've never bothered with measuring case capacity.
Some benchrest shooters may do it.
I dont think a beginner reloader should be concerned with it even slightly.

Just to clarify the post of grandpamac that's not case volume hes referring to case weight. I don't think you could squeeze 155 grains of powder into a case smaller than a 50 cal bmg

and your case SIZE will also make a difference...eg 223 case will matter more if 2 grns different capacity than a 270/36-06 sized case..the percentage of difference will be less
now me personally have never really worried about it..call me lazy but my two main rifles for last 25 years have both been VERY unfussy.... whatever they were fed ,within reason, they both will group them in useful sized group.
the most dramatic test we did was over bench to eliminate human factor and we fired 10 different loads through my .270 every thing from 110grns-160grn projectile size and group was easily covered by playing card 2" wide 3" high...if we had taken out the 2 hottest loads both 130grn...one winchester silver tip the other a norma SP the group was closer to 2".plenty good enough for sub 200yard shoulder shooting.

@grandpamac a bit of light reading for you. Assuming you can access the file.

Case Weighing.pdf

Originally Posted by zimmer

@grandpamac a bit of light reading for you. Assuming you can access the file.

Attachment 167400

Greetings Zimmer,
Interesting stuff. I never thought case weighing was any better than volume measurements and possibly not quite as good. It was just a damned sight more convenient. I use it mainly to identify batches of cases with the same head stamp that are close in capacity to a batch with a different head stamp. This aids keeping track of the batches so they all have the same number of firings, trimmings and so on.
Regards Grandpamac.