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As a cost conscious service rifle match competitor, I scavenge 308 Winchester / 7.62 x 51 mm range brass. I sort the brass by manufacturer, I size it, de-prime it, tumble it clean and weigh it.

The weight of brass and the uniformity of a manufacturer’s brass weight will influence chamber pressure and bullet velocity. Brass weight can also influence the cost of competing.

My accumulated stockpile of brass includes the following manufacturers: CBC (Companhia Brasileira de Cartuchos), Federal, GFL (Giulio Fiocchi), Hornady Match, Lake City Match (NM 68, NM 77 and Match 91) PMC (Eldorado Cartridge Corporation—previously Patton and Morgan Corporation and Pan Metal Corporation), PPU (Prvi Partizan) WCC (Western Cartridge Company), and Winchester. I have found very little RP, Norma or Wolf brass.
The Mean weight in grains of the listed manufacturers brass is as follows: Winchester at 157.13, Winchester nickel plated at 159.82, Hornady Match at 166.29, PPU at 166.94, Federal 308 WIN at 176.90, Lake City NM 68 at 177.55, Lake City Match 91 at 177.98, Lake City Match 77 at 178.45, GFL at 178.89, WCC at 179.48, PMC at 179.50 and CBC Nato 12 at 183.09.

As you can see Winchester’s mean weight is the lightest at 157.13 grains, even when nickel plated it only weights 159.82 grains, and CBC Nato 72’s mean weight is the heaviest at 183.09 grains. That is a range of 25.95 grains.

These weights are important because the American Rifleman recommends that powder charge be reduced by 1 grain for every 11 grains of empty case weight. This translates as 17 grains more brass weight requires 1½ grains less powder. For example if I am loading 42 grains of IMR 4895 in a Winchester brass—mean weight of 157 grains—and switch to Federal brass—mean weight of 176 grains—I should reduce my IMR 4895 load to 40.5 grains to avoid excess chamber pressure.

There are 7000 grains in one (1) pound of IMR 4895 which costs about $30. Therefore with a 40.5 grain load, I can get 172 rounds at $.17 each with a 42 grain load I can get 166 rounds at $.18 each in powder cost.

Accuracy is influenced by consistency. A wide variation in weight of a specific manufacturer’s brass may influence the consistency of camber pressure and thus bullet velocity.

The weight Standard Deviation by manufacturer is as follows: Federal 308 WIN at .633, GFL at .635, Lake City Match 91 at .691, WCC at .755, PMC at .873, Lake City NM 68 at 1.072, Winchester nickel plated at 1.083, Lake City Match 77 at 1.083, PPU at 1.462, CBC Nato 12 at 1.557, Winchester at 1.911, Hornady Match at 2.342.

The weight Standard Deviation is lowest for Federal at .633 with GFL close at .635 and highest for Hornady Match at 2.342. It appears Federal has a more uniform weight and Hornady Match has the least uniform weight. If uniform weight is an indication of uniform case capacity, then Federal is the most uniform and Hornady Match is the least uniform.

Shot to shot consistency is important when competing. If uniform brass weight means uniform case capacity then chamber pressure and bullet velocity will produce more consistent—accurate—ammunition.
According to Brownells’ website, Federal 308 Winchester goes for $26 per 50 or $. 52 per and Hornady 308 Winchester Match goes for $35 per 50 or $ .70 per.

Federal brass is less expensive, has greater weight uniformity and less case capacity which means I can get the velocity I need with a smaller powder charge. For an 800 point service rifle match, I can use rounds that cost $ .69 per round using Federal brass as opposed to $ .88 per round with Hornady Match. That will save me $16.72 per match. The cost of bullets and primers are not factored into this cost.

This is in no way a scientific survey nor can inferences be deduced from my findings, but it might be useful to service rifle competitors and the re-loading community.
 

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Robert

Thanks for all of your work in compiling that data. And special thanks for sharing it.

I really hesitate to even bring this up, but how about a little additional research? In particular, some comparisons of case capacity vs. case weight. There are times when weight does not correlate with capacity. It only takes a test of 1 or 2 of each case to see a pattern. To me, capacity is much more important when interpolating powder charges.

As I said, it's bold of me to suggest that you do some more work for us so just ignore me if you want.

Ray
 

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I lost all of my rifles & handguns in a mishap on Rio Grande when the barge hit a sandbar and sank.
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Very interesting read robert Harrison, your research into the weights of brass and powder charges makes a lot of since. Thanks for your thread here.

DI5
 

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Robert

Thanks for all of your work in compiling that data. And special thanks for sharing it.

I really hesitate to even bring this up, but how about a little additional research? In particular, some comparisons of case capacity vs. case weight. There are times when weight does not correlate with capacity. It only takes a test of 1 or 2 of each case to see a pattern. To me, capacity is much more important when interpolating powder charges.

As I said, it's bold of me to suggest that you do some more work for us so just ignore me if you want.

Ray
Very well said. Keep seeing threads on brass weight rather than volume.

I sort by head stamp and (maybe) by year on LC brass only as a very rough way of reducing significant volume variations. I realize this is still not the most accurate sorting method but is fine for me as I am not after 0.1-0.2" group improvement. I do not shoot competition nor go to the range to kill paper looking for tightest possible groups. I may put some attention to do a dozen brass just to see if the recipe gives good or better group. My rifles are mainly hunting and varmint shooting plus some range time to do a bit of load testing. If my rifle is basically a 1 1/2 MOA performer, then I look at loads that will give me close to that and whatever velocity I can get. If I was looking at super tight group then I would concentrate on volume uniformity more.
 

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I do use case volume as my guiding factor for commercial brass. Then match tune the primer pocket/sprue hole, turn the case necks and set OAL's. Most military brass is significantly thicker and is usually different in volume compared to commercial brass.

For match brass, especially nickel plated brass, it has bee my experience that is in a different category than other brass as it is made to tighter specs.
 

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Thanks Robert, for the info and work you put into this. Very Helpful; infact, You may have answered a question that I had from my last range trip where I chorno'd both Federal GMMs and Hornady Match rounds. The Federals had pretty tight numbers Such as 41 FPS ES and 13 SD and the Hornady's had some pretty bad numbers such as 220 ES and 91 SD--at first I thought I was getting errors with my chrono, but these readings remained as such through two boxes of rounds each.

Your findings are consistent with and could explain my findings.

Thanks again.
 

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Robert

Thanks for all of your work in compiling that data. And special thanks for sharing it.

I really hesitate to even bring this up, but how about a little additional research? In particular, some comparisons of case capacity vs. case weight. There are times when weight does not correlate with capacity. It only takes a test of 1 or 2 of each case to see a pattern. To me, capacity is much more important when interpolating powder charges.

As I said, it's bold of me to suggest that you do some more work for us so just ignore me if you want.

Ray
There would be inconsistencies comparing weight to capacities, because capacities depend on the factory preparation dies, or whether once fired, whether AS FIRED or sized, and the dimensional configuration of the chamber.

For instance, I have made measurements on .308 FGMM cases, SB RCBS sized cases, and Regular RCBS sized cases. The FGMM cases are the smallest diameter (stands to reason since Federal want their factory cases to fit even the smallest chambers); SB RCBS sized 1X FGMM is next larger diameter; Regular RCBS sized 1X is next larger diameter. AS FIRED is usually going to be even larger diameter.

Case volume varies with the square of the diameter dimension, varies only linearly with the length dimension.
 
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My point was a simple one, more in line with my ignorant farm-boy education. That is, more brass in the case (heavier weight), does not always correlate with less internal capacity. It's easy and quick to verify. In truth, I seldom weigh brass except to weed out really bad cases. I check and record comparative capacities. Many others that I shoot with do the same. That's how we have come to refer to different case brands and/or shapes as a "50-grain case", etc. In addition, most ballistic calculators start with the basic input of case capacity.

But, YMMV.

Ray
 

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Robert....... Thank you for the detailed information. I will bookmark it for future reference.

A few questions. Are you shooting a bolt gun or a semi-auto?

In applying your findings .... Is it more noticeable in a bolt gun than a semi-auto?

Using your findings and reloading.... What is the best results you could expect if you did everything perfect? What would be the worst MOA results if all the variables were mismatched?

Again..... Thank you,

Hobo
 

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Here you go........

Here is what I get for case capacities.

Lake City.
63 56.2
64 54.4
65 55.3
68 57.4
69 55.8
73 54
74 54.7
75 54.6
76 55.6
81 54.6
82 54.7
87 54.8
02 54.5
03 55
05 55

LC Match
65 54.5
66 55.3
72 55
79 54.9
81 55.4

LC Long Range
02 54
03 55.1
04 55
05 54.9
06 55.6

WRA
*1958 commercial case 59.2
66 55.3
68 55.2
70 55.6
84 55.2

RA
69 50.6 yea its small

IVI
68 55
69 55.6

TW
69 54.1

PMC 53.9

Odd balls
IK 85 55.4
PS 82 54.3
INDMIL 84 56.1
Frontier 56.2
PPU 55.8
CBC 54.5

Commercial
FC 54.8
REM-PETE 55.2
Win 308 57.0
 

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My point was a simple one, more in line with my ignorant farm-boy education. That is, more brass in the case (heavier weight), does not always correlate with less internal capacity. It's easy and quick to verify. In truth, I seldom weigh brass except to weed out really bad cases. I check and record comparative capacities. Many others that I shoot with do the same. That's how we have come to refer to different case brands and/or shapes as a "50-grain case", etc. In addition, most ballistic calculators start with the basic input of case capacity.

But, YMMV.

Ray
I agree 100%. In my own inept way, I was trying to point out some of the possible reasons for your observation that case capacity does not necessarily track case weight.BGRIN1

IMO, using your AS FIRED case volume from the chamber of your rifle, is the most accurate way to run the calculations.
 

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Unfortunately there is no correlation between case weight and volume. Some time ago I ran across a study done by Robert Johnson entitled "Case Mass vs. Case Volume" in which he analyzes the relationship between case mass (weight) and volume of .308 Lapua cases. Using 71 cases he selected cases two different ways, first by selecting cases that weighed within a specific range and then by selecting cases that had volumes within a specific range. In the end he showed smaller groups and better standard deviations with cases that were grouped by volume rather than by weight. He also created on chart that proves that case weight and volume do not correlate.



The diamonds represent each case and this chart shows case weights vs. mass. Notice that a case volume of 55.2 grains of water appears across almost all of the case weights; that means that regardless of the weight of most of the cases there were many that had the same volume. Therefore, the case weight does not correlate to the case volume in any reliable manner.

Link to the study

I do separate my brass in ranges of 1 grain of weight but only within the same brand and lot number. I figure that within a single lot of any specific brand creating weight groups is a faster way to limit volume variation rather than going through the process of determining volume for each case. I make the assumption that the manufacturer tried to keep the volume pretty consistent within that single lot so my weight groups should simply improve volume variation just a little more.
 
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Discussion Starter · #16 ·
RAMMAC

I found the article “Case Mass vs. Case Volume” very informative, and I appreciate your reference to it. It is now part of my reloading research file. I agree with Johnson that uniform case volume is a better indicator of consistency and accuracy than is case weight. But…

Johnson’s thesis is “The thickness of brass has a direct relation to the volume of the case and the heavier the case the thicker the brass, therefore less case volume.” This thesis is a self-evident truth because the SAAMI exterior case dimensions for a 308 Winchester cartridge are uniform regardless of the manufacturer: The case length is 2.015” to 2.020”, shoulder angle is 20o, rim thickness is .055” to .065”, etc. The only variables are brass alloy and brass thickness.

Unfortunately Johnson’s research design to test the thesis is flawed. Using only one manufacturer—Lapua—does not test his thesis. To test his thesis, he would need to compare cases made by several manufacturers. This has been done with Lapua, Winchester Western and Lake City NM 81 brass. (http://thefiringline.com post by mehavey titled “Case weight vs Volume” posted June 3, 2012). The author identified a “linear relationship” between “case weight” and “case volume” concluding “the lighter the case the greater the volume.”

I will test the thesis using Winchester, CBC NATO 12 and Federal cases. In my research, Winchester was the lightest, CBC was the heaviest and Federal had the smallest standard deviation of the cases weighed.
 

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Discussion Starter · #17 ·
Hobo Hilton,

I shoot only an M-1A built with USGI parts except receiver. I only use the heavy cases, 178 grains or heavier as the M-1A is hard on brass. Also, I shoot service rifle matches, so I don't have benchrest accuracy tests.

Thx,

Bob...
 

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Unfortunately Johnson’s research design to test the thesis is flawed. Using only one manufacturer—Lapua—does not test his thesis.
I disagree. The point of the test was to prove or disprove the idea that case mass was directly related to case volume. Using only one brand of case reduced the variables, different cases will interject the possibility that differences in brass composition could effect the results. Using the same brand case eliminated that possibility.
 

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Thanks RAMMAC for the article. Think about this for a moment.Maybe the difference in weight is in the case head rather than in the sidewall of the cartridge. This would account for a weight difference, but no change in the actual volume???? Maybe I'm being anal in sorting my same lot number GGG into .5 gr lots after completing resizeing, PP prep, and trimming. dozier
 
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