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Old October 16, 2012, 03:07 PM   #1
NWPilgrim
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Question about ACTUAL case capacities...

I am wondering about the actual case capacities based on headstamp, and if I am measuring correctly.

I have read in numerous places the guideline that military brass is thick and less case capacity so download y 1-2 grains. I understand that case weight is not a good indicator of capacity because the extra brass can e in the head and not the case wall, etc.

I finally got around to actually measuring case capacities and was surprised by the results. I had my brass sorted by headstamp (NOT year for military brass as it seemed consistent at least in weight) and had found the approximate average weight for each headstamp.

Method I used
So I took a case weighing near the average for each headstamp and seated a primer and trickled in water to fill it completely. I then dumped the water from the case into a pan on the zeroed electronic scale (+/1 0.1 gr). All cases were sized and trimmed to the same dimensions.

SEE UPDATED RESULTS IN POST #6

.30-06 Results in Grains of Water
Military
- LC = 67.9
- SL = 67.7
- WCC = 67.6
- HXP = 67.5
- TW = 66.3 (only significant variance)

Averages about 67.7 gr. for all but TW.

Commercial
- R-P = 67.5
- Win = 67.5
Might pull some Federal ammo just to measure the cases while I am thinking about it.


Now in QuickLoad it states to measure the capacity of a fired, UNsized case, but I would think at least for headstamp comparisons it is valid to use sized cases. QL using the fired case size for computing the actual pressure.

Questions
Is there any definitive reference for case capacities, that is, with actual measurements? From my measurements I cannot see ANY significant difference between R-P and Winchester commercial cases and military cases except of course TW. Do I have unusual cases, measured incorrectly, or is the old adage wrong or outdated? My military cases range from 1953 through 1970.


So then I did the same thing for .223, except due to the water surface tension I did not seat a primer but just held my thumb of the primer hole and released it to pour out the water.

.223/5.56 Results in Grains of Water
Military
- LC = 30.0
- WCC = 30.0
- MAI = 30.0
- CJ = 29.9
- TW = 29.5 (again, the only outlier, slightly)

Commercial
- FC small = 30.4
- FC large = 30.2
- PMC = 30.1
- Win = 29.7
- Fiocchi = 29.7
- R-P = 29.6
- S&B = 28.7 (significant outlier)


In the case of .223 versus 5.56 it appears the military brass has less spread and is near the top of capacity (contrary to popular guideline), and the commercial ranges from the military capacity to much less.

I am thinking that except for a couple of headstamps the military and commercial brass has practically the same capacities even though the weights vary widely. These were single samples taken from the weight averages from hundreds of cases (at least 50 of any one headstamp and some were hundreds of cases).

Any problem with my method, results or tentative conclusion?
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Last edited by NWPilgrim; October 16, 2012 at 07:37 PM.
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Old October 16, 2012, 03:10 PM   #2
Brian Pfleuger
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The only thing I'd be curious about is why you would bother dumping the water in a pan. It seems like it might leave some water stuck to the case walls. I always zero the scale with the empty case and then weigh it full of water.
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Old October 16, 2012, 03:29 PM   #3
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Fired capacity is closer to the volume the case actually gives the powder in your chamber because it expands to touch the chamber walls before the pressure peaks, unless you are loading below around 30,000 psi. Measuring the resized capacity is good to learn when your load will actually start to compress powder or to determine pressure when you fire the round in your sizing die instead of your gun (not recommended).

Figure to have to change powder charge between 0.06 and 0.07 grains for each grain of case weight difference, assuming outside dimensions are all the same.

Difference in military case capacity and commercial case capacity is only significant in .308/7.62. As you've discovered, .30-06 and, especially, .223/5.56 need little to no compensation for brand as far as powder charge is concerned. In .308/7.62 I've seen up to 3.5 grains water capacity difference in some makes. Thats about 30 grains of brass weight difference or around 2 grains powder charge difference to keep the same barrel time and in the same peak pressure range.
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Old October 16, 2012, 04:26 PM   #4
NWPilgrim
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Thanks for the feedback guys! I guess I measured water that way because that is how I weigh powder. I'll try it in the case and see if any difference. But, I would think if I had water adhering to the case I would get erratic measurements, not so many that were nearly the same.

Thanks Unclenick for confirming about .30-06 and .223. I still find this warning in reloading manuals and wonder how something could be passed around for so long when even cases from 1953 through 2010 do not support this. I haven't loaded .308 for a long time so when I get back to it I will measure those as well.

Anyone have their own case capacity measurements to compare? I would be interested to see how mine correlate and what other headstamps look like. If my capacities change using Peetza's method I'll repost or update the original.
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Old October 16, 2012, 04:54 PM   #5
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Folks checking case capacity with water should select ten with the same volume then get 10 with the same weight in grains, then ten more within 1% in weight, load them with exact charge weights for a given bullet. Shoot them through a chronograph and see what the velocity spread is.
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Old October 16, 2012, 07:36 PM   #6
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OK, I changed the weighing method to weigh empty case, fill with water and weigh the filled case on scale, subtract original empty weight to get weight of water in grains.

Again, this is just an informal comparison of RELATIVE case capacities to investigate any difference between military and commercial brass in .30-06 and .223. I am not attempting to measure the actual fired case volume for use in pressure calculations. While this is not a statistically valid sampling, the samples selected were representative of their headstamps for my purposes. I would consider anything within 0.5 grains as insignificant for relative comparisons.

New results for .30-06
Headstamp, empty case gr., water gr.

Military cases
HXP____194.0___68.8---[outlier]
WCC___193.0___68.0
SL_____197.3___68.0
LC_____198.9___67.9
TW____198.9___67.8

Commercial
Win____192.8___68.3
R-P____200.9___68.0


Considering the empty weights varied from 193 gr - 200.9 gr, it is surprising that water capacity only varied 67.8 - 68.3 gr except for the HXP and the two extreme empty weights had exactly the same water weight.

New results for ..223/5.56
Results in Grains of Water

Military
LC____95.2___31.0---[outlier]
WCC__95.9___30.4
CJ____96.6___30.4
MAI___97.1___30.4
TW___97.1___30.2

Commercial
PMC______95.2___30.8---[outlier]
FC small___94.4___30.6
FC large___96.6___30.4
Win______96.1___30.2
R-P______94.2___30.1
Fiocchi___101.5___29.9
S&B_____107.0___29.2---[outlier]

Overall, this seems to confirm at least informally there is no significant difference BETWEEN MILITARY AND COMMERCIAL case capacity for these two cartridges. There is more variation within either military or commercial than between the two types.

Welcome any additional data points others want to share on their own measurements or findings.
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Last edited by Unclenick; October 17, 2012 at 01:13 PM. Reason: Fixed data lable from .30-06 duplicate to .223/5.56
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Old October 17, 2012, 01:22 PM   #7
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The different weights having similar capacity can be accounted for by differences in exterior dimensions. The caveat, when using weight to determine capacities, is that the outside dimensions be the same.
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Old October 17, 2012, 02:38 PM   #8
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They were all sized in the same die and trimmed to the same length, per cartridge.

So if it has same interior capacity and different weight it must be different mass in the head area.
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Old October 17, 2012, 04:34 PM   #9
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Unclenick is right about capacity vs weight being valid only when outside case dimensions are the same. This happens one other place besides in a die. . .in the chamber at peak pressure.

Sierra Bullets has no problem getting sub 1/4 moa with 30 caliber match bullets at 200 yards from .308 and .300 Win mag cases with a 2% spread in case weight and thrown charges. I don't think case weight within a given lot is too important as long as its in a 3% spread.

As arsenal match ammo with such spreads in case weight and capacity gets sub 1/3 moa at worst at 100 yards (and 1 moa at 600), reloaded ammo with the same thing not doing as well has bigger variables elsewhere.

Last edited by Bart B.; October 18, 2012 at 09:03 AM.
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Old October 18, 2012, 04:58 PM   #10
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NWPilgrim,

Yes. Head diameters, extractor groove depth, forward angle off the extractor groove, etc. These all have tolerances. The sizing die has a radiused mouth and it stops on a shell holder deck 0.125" above the breech end of the case, so the sizing isn't actually getting all the way to the head, normally. But the brass itself, AFAIK is all 70:30 cartridge brass that has a specific gravity of 8.53. I just don't know what the tolerance for that is. If you want to get really scienterrific about it, the water displacement of the case brass has to be measured.


Bart B,

That sounds about right. In .308 Winchester, if I plug a 3% brass weight change into a typical 170 grain commercial case weight shooting the 175 grain SMK over IMR 4895 to 2640 fps from a 24" tube, it only takes about 0.2 grains of powder charge change to keep velocity constant. So figure that if your brass weight is in the center of the range, that's like a ±0.1 grain powder charge difference as far as velocity drop on target is concerned. It was about 15 fps difference in the simulator. Still well within normal muzzle velocity extreme spread for a load, even if the charges were weighed.
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Old October 18, 2012, 06:40 PM   #11
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One other thing on case capacity vs weight. Perfectly round ones for a given weight have more capacity than oval shaped ones. If ones oval shape was reduced to totally flattened, capacity would be zero.
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Old October 20, 2012, 10:28 PM   #12
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NWPilgrim, I have weighed cases for my benefit, and I heard all the deductive reasoning and rational about being thicker and because they? are thicker they are heavier. I had absolutely no interest in volume, I have about the same interest in volume as I do seating the bullet .002” off the lands, I am the fan of the running start, I want my bullets to have “THE JUMP”.

Instead of me, myself and I checking volume, first I weighed 250 cases then sorted by head stamps, after sorting I measured the case thickness, first, the case head, all my military cases with the exception of anything made by Wester my military case heads measured .200” +/- very little, so, before I take someone serious when they tell me there is no difference I have to insist there must be a difference in the length of the powder column then through deductive reasoning they must consider if the military case has less capacity the reduced capacity must be in the thickness of the case wall.

So I decided the powder column in my military cases was longer in length and smaller in diameter than in the R-P case. I measured the case head thickness of 100 R-P case heads, the thickness was .260”+, deductive reasoning caused me to decide the thick case head reduced the length of the powder column and if the length of the column was shorter but held more powder, I then concluded the R-P powder column for the 30/06 cases was shorter in length but larger in diameter than the powder column in my military cases.

Then I decided when shooting heavy loads the R-P case was a better choice because of the thicker case head, for the most part by .060” when compressing the case head the .060” takes more compression before catastrophic failure, for everything else, I do not mix case head stamps.

Then there is the 308W and the 30/06, the 308W is an impressive performer when compared with the 30/06, the powder column of the 308W is shorter in length and larger in diameter than the powder column of the 30/06.

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Old October 21, 2012, 08:05 AM   #13
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Just a cpl thoughts on this...and I too have oft heard of the thickness of military brass...that warning is mentioned in Ken Waters "Pet Loads" books as well as "Hatcher's Notebook", and "Handloading" the NRA's excellent book on the subject, by William C. Davis...all authoritative tomes.

The NRA's "Handloading" book, now out of print I think, was published in 1981 and updated in 1986. On page 134, in an article on the effects of component changes, one table collates velocity changes vs. weight differences given identical other loading components. Weights varied from a low of 189 gr for Western, to a high of 214.1 for Peters. Velocities varied from 2570 to 2672 fps. The table also tabulated weight variance within each brand...some as high as 7.0 to 8.0 gr, with high differences in both military and commercial brass.

My experience is with .30-06 and 5.56mm rounds, both military and commercial. From that experience, I can say that military brass does produce add'l velocity, on average, than commercial. Is that due to reduced internal capacity, or to another factor not considered; here are some ideas: flash hole size and regularity, primer pocket thickness, strength of the annealed portion of the shoulder and neck, and brass quality/composition. There are others most probably, that I've overlooked. As to the reason for that add'l velocity, I can't say, other than the fact that it equates to higher pressures.

I will opine that based on NRA's studies, some of it 20+ years old now, that brass can and will differ in thickness, among other characteristics, and can affect pressures. Too, I have no confidence that modern ammunition brass cases are significantly better with quality control than they were 20+ years ago. The old caveat, start well below max and work up slowly still rings true.

A good discussion NWPilgrim...thanks for bringing it up. Best Regards, Rod
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Old October 21, 2012, 11:37 AM   #14
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“Just a cpl thoughts on this...and I too have oft heard of the thickness of military brass...that warning is mentioned in Ken Waters "Pet Loads" books as well as "Hatcher's Notebook", and "Hand loading" the NRA's excellent book on the subject, by William C. Davis...all authoritative tomes”

There are those that talk about it and then there are the others. I claim to have never read "Hatcher's Notebook", to claim to have read his books/arricles would force me to agree or be accused of not being able to comprehend what I read.
Ken Waters and Hatcher at best could only be half right (correct), again, I measured the case head thickness from the head of the case to the bottom of the cup (above the web), all my military case heads measured .200”, I measured the case head thickness of R-P cases, the thickness of the R-P case head from the usual place measured .260”. Rational for being half wrong or half correct, my military cases have thin case heads, I can not apply the ‘military case is thicker’ to my cases, my case heads are thinner.

Flash hole diameter, there is one member on this forum that starts with ‘unfirming the diameter of his flash holes’ rational? For starters, just in case it matters, the other, measure before and again after, if the primer pocket opens up the flash hole can open up, the reloader that has no clue as to the diameter of the flash hole in the big inning is left with determining the effect of pressure from the outside, then there is the problem of measuring case head diameter with bladed micrometers.

A better article was written 20+ years earlier, I was the only one that read the article, a shooter, reloader gun enthuses wrote an article about his experience with case testing. He purchased 500 cases from one lot from one manufacturer. He did not purchase 500 cases from each manufacturer for a comparison, he purchased 500 cases from one manufacturer then made his comparison using one rifle. After firing and measuring, sorting and testing again, he settled on 47 cases +/- very few. Other cases he found he could index the cases in the chamber and get the same accuracy every time, rotating the case changed the point of impact. Then there were cases that had a powder column that was not concentric, case necks that were not concentric. He measured the case head and wall thickness.

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Old October 22, 2012, 03:04 PM   #15
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Rodfac, I agree with your findings on case weight vs velocity.

Using the same powder charge, primer and bullet seated with the same neck tension and OAL in .308 Win. cases weighing 149 (WCC58 headstamp) to 185 (weird foriegn military headstamp) grains, there was about a 70 fps spread in average muzzle velocity.
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Old October 24, 2012, 09:23 PM   #16
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Thanks Bart.

Another good book on precision loading, with up to date, modern tools is Glenn Zediker's, "Handloading for Competition". His discussion runs to over 400 pages and exhaustively covers all aspects of precision loading. His chapters on tools, and case preparation for use at long range are especially notable.

If you're going to shoot the .223 or .308 "over the course" in CMP and NRA competition, you'll find his narrative useful; but his methods and the descriptions of the tools available are useful for any shooter striving for better accuracy...check out case selection for use on the 600 yd. line...made a believer of me!

Not to pull your chain too hard, Mr. Guffy...but I really do get higher velocities with military brass! Best Regards, Rod
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Old October 26, 2012, 10:38 AM   #17
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Rodfac, I think most folks spend too much time trying to unifom the minute irregular details on cartridge cases. There are top level competitors who don't do any case prep at all and get the same accuracy as those to do everything possible to eliminate any difference between cases.

Sierra Bullets, for one, does no case prep at all on their cases used to test their stuff for accuracy. Their best match bullets to into 1/4 MOA or better at 200 yards with metered, not weighed, powder charges.
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