Is 5.56x45 military brass thicker than .223 commercial brass?

[uscra112]

Every so often I read that loads for military brass have to be reduced compared to loads in commercial brass, on the theory that military brass is thicker.

Having a reasonably accurate digital scale, and having a couple thousand mixed .223/5.56 "range-brass" cases in hand, I thought I'd see. So I weighed all 2000 of 'em, sorting them into three groups. All the cases had been deprimed, sized, pin-tumbled and well dried. The four largest lots are:

836 pieces Lake City of varying years, from 1990 to 2011
323 pieces WCC (Military 5.56)
353 pieces R-P commercial
285 pieces Federal commercial

Here's how the lots sorted out.

........Light........Normal........Heavy
____89-91.9__91.0-92.9___93.0-95+ (grains)

LC____31_______778_________27_____93.1% within "normal" range

WCC__21_______263_________39_____81.4%

R-P___19_______313_________21_____88.7%

FC____19_______289_________29_____83.2%

I took five cases weighing within 0.3 grains of each other out of each lot and did the water test. Not surprisingly, the water capacities were 30.0 to 30.2 grains across all four lots, full to the top with a slight concave meniscus. (I used a strong light to compare the meniscus form, to be sure that I hadn't over or underfilled any.) Now, 0.2 grains variance in water capacity, using a near max load of Varget, (26.4 grains for a 62 grain M855), results in about 1000 psi variance in peak pressure as calculated by Quickload.

Then I took two cases weighing 90.0 and 95.9 grains respectively, (both headstamped FC), and found the water capacities. 30.7 and 29.9 respectively. Same exact results when I picked out two WCC cases having the same dry weights. The Quickload calculation now says 4300 psi variance. Weight sorting to get rid of these outliers seems warranted.

Based on this sample, it would appear that, for the .223/5.56 cartridge, Lake City and WCC brass are not heavier, nor do they have less capacity, on average, than R-P or Federal commercial .223 brass. It also seems to me that that variance, (within the WCC and Federal lots especially), is a lot more significant than the difference in the probable average weights of the four lots. (I did not have the patience to log the weight of every case so I could calculate actual averages and standard deviations. There are scales that will talk to a database, but I can't afford one.)

Finally, I had a number of odds and sods - PMC, Speer, TZZ, Winchester, S&B, PSD, FC military, which were few enough that I'm not including them in the main analysis.
PSD - 17 of 25 were over 93 grains!
PMC - 30 of 31 in the middle range, one was 93.0 and only five were below 92.0.
S&B - 15 of 15 within the middle cohort.
Wish I had bigger samples of those two.

YMMV of course.

[William Yanda]

Thanks for the post. I had the impression from my reading, here and elsewhere that the "military brass is heavier" was probably more applicable to 7.62 than 5.56. Any 7.62 reloaders confirm?
Bill

[Larry Gibson]

I can confirm it is more applicable to US made 30-06 and 7.62 NATO. Foreign made stuff varies appreciably and each lot of that should be weighed and compared.

Larry Gibson

[1Shirt]

IMO, some is, some isn't! If you mix lots you will find variance in both military and commercial. Sometimes it is minimal, and at other times appreciable.
1Shirt!

[felix]

Brass is a mixture of zinc and copper. Zinc is the element which provides the toughness to the cases. The more zinc, the more yellow the cases. The more zinc, the lighter weight are the cases. So, the case capacity can easily be "the same" no matter the lot, which suggests even more the difference in cases should be determined by the target grouping of those selected. ... felix

[felix]

Brass is a mixture of zinc and copper. Zinc is the element which provides the toughness to the cases. The more zinc, the more yellow the cases. The more zinc, the lighter weight are the cases. So, the case capacity can easily be "the same" no matter the lot, which suggests even more the difference in cases should be determined by the target grouping of those selected. ... felix

[eck0313]

Federal .223 brass is among the heaviest, and it is soft compared to LC, or WWWC, or commerical Winchester. I don't even bother reloading Federal .223 brass.

[runfiverun]

i always trim the cases to the same length before trying stuff like this, it generaly will narrow down the curve.

[uscra112]

i always trim the cases to the same length before trying stuff like this, it generaly will narrow down the curve.

Good point. It would have reduced a potential variable had I trimmed 'em. If I have time over the holidays, I'll compare lengths out of the light and heavy groups to see if there's any trend. All of these were alleged to be 1x fired, so a measurement study would tell something about how well the various mfgrs hold that parameter in their process control scheme. Surely the mfgrs are including overall case length in their SPC plan, but I wonder if the MIL spec spells out the tolerance, or does it only specify tolerances for the characteristics of the assembled cartridge.

I should also have done a bigger sample of varying weights to get a better confidence level as to whether dry weight is a predictor of water capacity.

[Doc65]

YMMV, but I shot HighPower rifle matches in both Service Rifle & Match Rifle Catagory for a number of years a few years back, and found that their was little significant difference in the capacity of LC brass vs Win, Fed, R-P in 5.56/.223, there was a difference in the strength of the brass as the rather stiff load I was shooting for 600 yd were fine in the LC or Win, but would loosen the primer pockets in the Fed after a couple loadings, and even sooner in the R-P cases.

With that said I do find that while I really LIKE the LC 7.62x51 brass(especially the match brass with the little circle with a cross in it on the headstamp) I cannot use the same loads in it that I can in once fired Fed GMM brass, or Nosler Custom brass, or Lapua Brass(those are the only ones I have in any kind of quantity). All the commercial brass is pretty close on capacity with the Lapua being the smallest capacity(though VERY uniform & true)

[uscra112]

Dug out the .30-06 brass I have. Only LC Match and FC civilian. Weighed 20 of each. All I have time for. . .

LC Match avg. weight 193.8 grains, S.D. 1.2 extreme spread 5.1 grains

FC .30-06 avg. weight 197.5 grains, S.D. 1.6 extreme spread 6.9 grains

Just one instance, but darn if it ain't the civvy brass that's quite a bit heavier.

[felix]

No tellin' how much scrap brass is being used in the final brass mixture these days for a cartridge run. The problem exists in the purity of the scrap used. Very well could be some foreign elements deemed too costly to remove for the application. ... felix

[mdi]

Thanks for that test/report. I like to se real life numbers, rather than some vague refrence as to what someone said or may have done.

[Larry Gibson]

Dug out the .30-06 brass I have. Only LC Match and FC civilian. Weighed 20 of each. All I have time for. . .

LC Match avg. weight 193.8 grains, S.D. 1.2 extreme spread 5.1 grains

FC .30-06 avg. weight 197.5 grains, S.D. 1.6 extreme spread 6.9 grains

Just one instance, but darn if it ain't the civvy brass that's quite a bit heavier.

WW cases will be considerably lighter in weight than either of those.

Larry Gibson

[quilbilly]

Since I resize a lot of my 223 cases to 7mmTCU, I don't care for the military cases since they split so easily on resizing because they seem to be more brittle. My favorites for resizing are S&B which rarely split (haven't done many in a while so that may have changed). Winchesters also resize well into 7mm.