I've been doing a little comparing of some .223 brass I have on-hand. Some is commercial Federal, some commercial PMC, some NATO that I bought as surplus loaded ammo a few years ago. The NATO is a mixture of carious years from LC, TZZ, and even a little WCC.

The point is that, weighing fired, cleaned, newly-primed, trimmed brass (all primers are CCI-450 from the same box), the FC brass weighs around 10 grains more than the NATO brass, BUT the capacity of both the FC and the NATO is ~31 grains of water. IOW, and in contrast to everything I've ever heard or read, the NATO 5.56mm brass is lighter than commercial .223, but its internal capacity is the same. The difference between the two is 8-10 grains.

Has anyone else run into this? What is/are the likely reason(s) for the military brass to be lighter yet have the same internal capacity?

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the density of brass is 8½ x that of water. So, brass that's 10 gr heavier will ony be able to hold 1.2 gr less water. Variations in overall dimensions are more important than a few grains difference in weight of brass.

You would have to first resize all the brass in the same resize dies, and trim them to length, to get the dimensions right before you weigh anything.

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MZ5, It is called deductive reasoning, military brass is heavier, therefore military brass is thicker, not true, just half true, military brass has a thinner web than commercial brass, the military 30/06 case has a web that is .200 thick commercial brass has a web thickness of .260 plus, (therefore) military, if heavier, has a thicker body than commercial cases, if this is true, the two cases are not the same if they weigh the same because the two columns of powder are different, the column of powder in the military case is longer and smaller in diameter then the powder column in the commercial case.

Deductive reasoning: When using the volume system for comparing difference between cases and or brands without checking thickness and weight, the information obtained may or may not be useful, even when checking cases from a box of 20 or a plastic bag of 50 or 100.


F. Guffey

Hmm. I disagree that they need to be sized in a reloading die rather than sized in my chamber (just a different type of die, if you will). I propose that I've done exactly what you propose. I've sized them all in the same "die" (my chamber), and as I said they're all trimmed the same.

I agree that with a powder like 748, for example, a 1.2 water-grains capacity difference should only amount to ~6,000 psi of chamber pressure difference and ~75 fps velocity difference. However, that equates to roughly a 0.8 grain powder charge weight increase from my current 26.6. That'll going to throw both my POI and my groups way out into the weeds (I've tried that kind of variation during work-ups).

Still, what I'm finding is that the interior volume of the brass is the same.

EDIT: NATO brass is thinner, but the case walls are thicker? I can't directly measure that very well. All I can do is measure neck thickness with my vernier calipers, and that's measuring the same for me. Don't know how reliable that is. In any event, I think I hear you to say, fguffey, that NATO brass is made in the Winchester style (i.e. the case head/web area is more capacious inside). Is that about it?

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Sized in your chamber.

Doesn't that require that they all expandced and contracted the same amount in order to end up with the same volume....which might not be true (and as brass hardness changes over time, the volume of brand new fired cases maight not match 8th time fired cases either).

I hear you, robbinstone, but wouldn't those same factors apply to brass sized with a sizer die just as much as they do to fire-formed? The sizing action is the same basic thing each way.

I don't suppose I'll spend much more time thinking about this, and I surely won't be buying any tools or equipment to satisfy this curiosity. It is just a very different observation from the conventional 'wisdom' which has a substantial impact on my handloading.

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My $0.02 on the matter is that the "weight" is different because of what the "brass" is made of. Do remember that the Gub-ment uses lowest bidder rules. And All brass is not made the same, A prime example is in water meters. Lead has long been used in the molds as a release agent. While the amount isn't large it does add to it, and they run a spec for, and against it.

Now do they use lead in rifle cases? maybe. But they may also have a different "mix" to make "brass" that meats the spec.

I agree however that sized in the chamber is the same as sized in a die.

It's not necessarily the same. Ribbonstone has a point in that military brass is typically harder and springier, so it may not come out of the chamber with the same exterior volume as the softer commercial counterpart. And Fguffy's point about the difference in some brass at the rim is a reminder that cases have tolerances. +0" and -0.008" in diameter of the head, for example, and the head does not expand with the rest of the case on firing. That tolerance can result in different external volume, all appearances to the contrary, and that would mess up the brass density-based calculation.

The way to tell is to take something like a .45-120 case or any other container that will hold a .223 case completely and won't exceed the capacity of your scale when it is full of water. Fill it about half or two thirds of the way with water. Set it on the scale in a powder pan or a small paper cup to catch overflow and note the total weight. Plug the mouth of your .223 case with clay and level it. Tie a loop of fine wire around the extractor groove and bend it so the case dangles straight up and down. Put a mark on the wire with a Sharpie which is the depth the wire will be submerged to. It must be close enough to the case so submerging to that mark will not let the .223 case touch the bottom of the container. Submerge the .223 case to the mark on the wire. If the case overflows into the pan or cup, that's OK, it won't affect the measurement. What you need to do is get the new weight with the case submerged but not touching the container. The additional weight shown on the scale under that condition will be the weight of the water displaced by the plugged .223 case and its wire. That weight increas will reflect the number of cubic centimeters of volume the exterior of the case has, plus that of the portion of the wire that is submerged. The wire doesn't matter because you are looking for a difference in displacement, not an accurate absolute volume. Repeat with the other case. The difference in the the two volume readings will tell the tale as far as exterior dimensions go.

You will be looking for a difference of just about 1.2 grains in the results for the two cases. That should register just fine on a powder scale. If you want to improve the accuracy of the measurement, you'll need to know the temperature of the water and adjust the result for its density at that temperature. There is a water density calculator here.

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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley

There is a simple solution to all of these brass related problems (or most of them) buy new unfired brass of known quality, and don't use anything but. I made the decision to do exactly that many years ago, and have never been sorry...in the long run, it's not a heckova lot more expensive, and it's a lot more comfortable loading brass that you know ..... I've used nothing but WW brass for many years, and have never had a bad case, not even one...it used to be much cheaper than it is now, so I stocked up on the stuff I shot a lot of .... I do pick up brass at the range, or wherever, but I give it away to friends.... and I'm not saying this to be "Holyier than thou",.. I just wanted to KNOW where my brass came from..... it's worked out well....

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OnWard .... the OL' OutLaw

Gubment sells to the lowest bidder, BUT that is once all of the bidders meet the standards as set out in the proposal. So, you can bet that something about the brass is spelled out in the contract.

The gubment just doesn't call up and say, send me send me 10 billions rounds of YOUR 5.56.

They call up and say we want 10 billion rounds of 5.56, BUILT THIS WAY, can ya do it? I don't know about the DOD, but the DHS tests ammo, and if it doesn't meet the specs they send it back and send them a bill.

Now, there may be some merit to what you say about the brass being dif, but not because of the lowest bid.

It's different because of machine guns. Actually, just saying it is harder isn't really specific enough. The heads and rims seem to be harder and the necks seem to need their first annealing sooner than commercial brass does, IME, but Hatcher refers to brass for automatic weapons having been softened between the wars to stretch more easily to help prevent head separations. He remarked that the softer brass caused problems in rapid fire in the Springfield '03 because it conformed more easily to the chamber and therefore extracted harder. As a result, special hard brass with an "R" (for rifle) added to the headstamp was made for the National Matches at that time, and kept separate from automatic weapons rounds. He claimed the soft brass was still being used as of 1947 when his Hatcher's Notebook was first published.

I don't know what the current spec is, but it should be obtainable since there isn't any sort of secrecy involved in small arms ammunition RFB's. I do know that it is loaded to a performance specification within a pressure range, rather than just to a simple pressure limit as civilian cartridges are. That is, it has a minimum and a maximum pressure and the bullet must reach a specified average velocity and/or muzzle energy from a test barrel when the powder charge produces a pressure within that range.

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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley

There is a school of thought to ignores weight completely and checks cases by volume. Some would bet that two cases of the same weight would have the same volume...be ready for a surprise.


I do keep my brass not only segregated by brand, but segregated by LOT and tend to volume check .22Hornet cases inside of each lot. There are ALWAYS a few rejects that get pitched in the "plinking" box.

With .308's, will keep the cases segregated by lot as well...not just the same headstamp, but from either the same box or from the same lot number. Those 1999 WCC cases do not have to match those 2003 WWC's (or anything else for that matter).

The vast majority of my loading ans shooting can be described as 'plinking"...i stand on my hind legs and shoot. a 1/2" differnce isn't going to really be noticed in the typical wobble of offhand shooting, but i do belive that if you get good at shooting off hand, EVERY other type of shooting is a breeze.