Is there a significant capacity difference in .223/5.56 brass

I've seen differences. I recently bought some Starline 223 brass which I know has less capacity than LC brass. When I weighed them, the Starline was ~100gn, the LC was ~92-93gn.

The lower capacity cases will give higher pressures for the same charge, so take that into account when you work up loads. I think if you work up loads with the lower capacity brass, you most likely will not have pressure problems when loading other brass. Unless you are looking for the utmost in accuracy, and are not at the top end of the charge range, you should be fine.

There is nearly zero difference between LC capacity and commercial for the 556/223.

There is often more variance from different brands or lots of commercial then there are between LC and commercial.

All depends on who mfg the brass. I've seen some mil 5.56 have < 5 gr difference in case capacity. I've also seen this much swing in commercial brass too. Going by dry weight may get you in the ball park. But in all cases the brass must all be in the same physical dimensions. So sized, trimmed to the same length. I prefer doing this on clean brass, inside and out. Heavier weight does not always means less capacity. It depends on where the weight is. If the necks are heavier wall it will weight heavier but does not impact the internal volume.

VoodooMountain said:

There is often more variance from different brands or lots of commercial then there are between LC and commercial.

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This mirrors my experience, but. . .

YOU (@Bbear) should measure for yourself. Once you size and trim, case weight correlates very well with internal capacity and is much easier to measure. Go ahead, measure 10 of each, and see what you find.

I spent several weeks last winter organizing, sorting, decapping and tumbling my brass stash. I have read so many threads like this one that I decided to weigh some 223/5.56 cases. I picked 100 cases from several headstamps and fully prepped them to load. That is, I resized them, trimmed them, uniformed the bottom of the primer pocket, deburred the flash hole, swaged any primer crimps and tumbled them. Then I weighed them.

GFL WCC16 Lapua BHA Match Winchester LC-12 FC(crimped) Perfecta Aguila PPU WCC-02 RP
Average weight 97.8 94.0 92.9 94.1 93.4 92.4 92.6 97.1 95.7 95.1 92.4 91.6
Heaviest 98.0 95.2 93.5 95.6 94.7 93.4 93.7 97.9 97.3 97.0 93.6 93.2
Lightest 96.3 92.9 92.6 93.3 92.5 91.5 91.7 96.2 94.6 93.8 91.0 90.5

A few notes on my procedures;
1.I felt that trimming the cases and prepping the primer pockets gave me a better idea of the end product.
2. These were random lots of 100 each, not hand picked, although I culled any with serious dents or road rash.
3. Cases were trimmed with A Giraud trimmer and test have shown that I usually maintain lengths to within .001.
4. Cases were weighed on a RCBS ChargeMaster.
5. The same resizing die and same case prep tools were used on all cases and by the same person (Me).
6. I did not measure the variation in neck wall thickness.
7. I did not cull any numbers once the 100 cases were prepped and weighed.

The test that I have done on other calibers showed that the heavier cases held less liquid (alcohol) by weight than the lighter cases. I did not weigh the liquid capacity of any of these. We should assume that other lots of the same headstamp may be different than these. I understand that 100 is a small sample and also that any real mathematicians here may be able to improve on my methods. Hope some of you find this interesting! Cabin fever can be either a good or bad thing!

Edit to add, the site scrambled my spread sheet for some reason. I had the numbers lined up much neater under the headstamps. Oh well!

lightman said:

I spent several weeks last winter organizing, sorting, decapping and tumbling my brass stash.

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Eek! Sorry to hear that man.
Do you mind stopping by the house if you're ever in the area though

Wouldn't it have more to do with volume than weight? I'm not claiming to know anything, but if different grades or brass stock suppliers use slightly different properties/alloys. This could account for slight differences. Just me thinking outloud, well, kinda.

Blue68f100 said:

All depends on who mfg the brass. I've seen some mil 5.56 have < 5 gr difference in case capacity. I've also seen this much swing in commercial brass too. Going by dry weight may get you in the ball park. But in all cases the brass must all be in the same physical dimensions. So sized, trimmed to the same length. I prefer doing this on clean brass, inside and out. Heavier weight does not always means less capacity. It depends on where the weight is. If the necks are heavier wall it will weight heavier but does not impact the internal volume.

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Wow, 5 gr. is quite a difference in case capacity for the 5.56.

Per Speer Manual #15: 223 has 31.9 grain H2O capacity, vs 5.56 case at 31.0 grain H2O capacity.

For general plinking/short target practice, no there isn't enough difference to matter.

If you're looking for extreme distance or accuracy, then ya, sorting by headstamp "might" help.