Rifle cases water capacity? Why?

C

Chainsaw.

New member
I get the point of using water capacity to measure cases volumetric capacity but, my question is when should the practice be applied? I JUST started reloading for long range precision stuff. I haven't even done my S.D grouping but a friend is hounding me to water measure my cases. I weighed them on a scale abd they are ALL with in 5 grains. Now call me crazy but if I have 200 doohikies, all made of the same material, all the same exact shape, could I no surmise that said doohikies would all weight pert-near the same? And being they would then could I also extrapolate that the internal volume of said doohikies all be pert-near the same?

I can see the usefulness of this practice but am I wrong in thinking I'm not even close to that point yet?
 
I have sorted my brass by headstamp and weight. After sizing the brass case length is checked and made uniform. 100 rounds of my winchester brass weighs within 2 grains. I put in a loading block in order by weight. Volumes that have been checked have been within .1 grain of water for any consecutive brass. My theory is that my method of case prep does not require volume checks if all else is made consistent.
 
How can you tell the internal volume of a vessel by it's weight?
Brass is an alloy of copper, zinc, and other metals.
Hopefully the mixture is right.

By the weight theory a ceramic container has the same volume as a plastic container. Although the ceramic container holds 1 pint of fluid and the plastic container holds 1 gallon.

Gross over exaturation, but you get the point.
 
The brass is of the same batch so the metal and manufacture are consistent. If it is resized to the same shape and still weighs the same random checks of volume give me the proof. I have not checked volume on my consistent brass other than for reference and random consistency checks. Those lots have has SDs of less than 10 fps when all else was performed consistently.
 
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Chainsaw,

I'm not sure if your friend is telling you to measure all of your cases for volume or not, but what you would do is measure say 5 of several different headstamp brass to get an idea as to the volumetric difference between headstamps. For example, by doing this with Lapua and Norma brass in .30-06, I found Norma was markedly lighter and had a much greater case capacity than the Lapua brass I had been using. Load development further told me that I needed to increase the powder charge by 0.7 of a grain with Norma brass to match the velocity I was getting with Lapua brass. Hope that helps.

Don
 
How can you tell the internal volume of a vessel by it's weight?
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Weigh it empty, then filled with distilled water, and do the math, although having done a lot of precision weighing in a laboratory I know it's not that simple if you're on a project that involves, say, hiding submarines - but plenty close enough for precision reloading.
 
Don you bring up an important point I forgot, all of my cases are the same head stamp, hornady, and so far there is a batch of 100, all bought together, then another 20 from a box of match ammo.

So, anyone want to address my questions in tje first post?:D
 
For long range precision shooting case weight means very little. Internal capacity is what matters. Your friend is correct
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For long range shooting, do you measure the volume of a fire formed case or a resized case? If you use Quickload, it recommends using fired volume for chamber pressures over 30,000 psi.

BTW, a specific case will weigh the same either fire formed or resized, but it's volume will differ significantly.
 
In my winchester brass a full length sized case holds 70.5 grains of H2O. A partial sized case holds 69.2 grains of water. That can be a difference of 15-35 fps depending on powder type, load and seating depth.
 
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Don't worry about any minute differences between individual cases that are all the same headstamp. Use the average of your headstamp's volumetric capacity in comparison to load data using another headstamp (i.e. load data using light Winchester brass and your Hornady brass, and adjust powder weight accordingly).

Don
 
Chainsaw:
Rifle cases water capacity? Why?
I get the point of using water capacity to measure cases volumetric capacity but, my question is when should the practice be applied? I JUST started reloading for long range precision stuff. I haven't even done my S.D grouping but a friend is hounding me to water measure my cases. I weighed them on a scale abd they are ALL with in 5 grains. Now call me crazy but if I have 200 doohikies, all made of the same material, all the same exact shape, could I no surmise that said doohikies would all weight pert-near the same? And being they would then could I also extrapolate that the internal volume of said doohikies all be pert-near the same?

I can see the usefulness of this practice but am I wrong in thinking I'm not even close to that point yet?
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Last summer I began a little science experiment which involves case capacity. Just so we understand the below numbers I will provide how the to date testing was done as for any test result data to have any value the procedure and method used need to be clearly stated.

I selected at random ten (10) cases each from at least five (5) large lots of brass. This afforded 50 cases selected at random. Each case was resized and deprimed and then cleaned, including cleaning the primer pockets. The brass was a mix of 308 Winchester and 7.62 NATO with the latter all having the same year of manufacture, WCC 10 and LC 13. Following resizing and uniform trimming to 2.005" with the idea being make the cases as uniform as possible. The sized cases were measured for OAL as well as distance from shoulder datum to case head and all cases were 1.630" +/- 0.002". However all cases again were an OAL of 2.005" and within 0.001". The idea being get the outside case dimensions as uniform as possible.

I weighed each case and the chart reflects (upper left quadrant) the case weights expressed in grains as grains is the unit of measure we all have come to know and love for powder charges. I then filled each case using a syringe and here I must confess to using tap water rater than distilled water. Now I confess distilled water would have been the better choice, however, based on previous test my own conclusion comes down to it really matters not as any difference in actual weight will not come into the end results. I also confess I did add a few (two) drops of dish washing liquid to about a gallon of tap water so there is another impurity. The dish washing liquid helps the full case come out even in the case neck, nice and level so all are uniform. None of this effects the water enough to matter in light of its intended use.

So here is what I ended up with:
Case%20Volume.png


The upper right quadrant reflects the case weights filled with water. The far right column reflects a "Tare" and the reason is I needed to obviously plug the flash holes. I used modeling clay, the same type used in glass bedding a stock, to plug the holes. The tare weight of 1.8 grains was subtracted from each case weight and I checked the weight of my small ball of clay between each group of ten (10) cases.

The lower left quadrant reflects the weight of each case with water added and finally the lower right quadrant reflects the calculated case volume for each case. The volume was calculated as follows. One gram of water occupies one cubic centimeter of water. While 1.00 cm ^ 3 = 1.00 grain of water @ 3.98 degrees C or 39.16 degrees F the numbers are close enough that it really matters not that I did this at about 68 degrees F.

Looking at all the numbers while amusing comes down to which of the five (5) samples was the better brass? My money is on the WCC 10 brass. Why? Because I am looking at "Standard Deviation" where the smaller the number the better. From a given lot the smaller the standard deviation the more uniform from case to case. So looking at those numbers when this brass is loaded, if we assume uniformity in loading weighing each charge and trickling down to some fractional part of a tenth of a grain, how much will it matter? Let's say I use a box of Sierra 168 grain Match King bullets (168 grain MKHP Match) how much will all this really matter? I plan to load them with AA 2495 powder and a charge of 40.0 grains as this delivers good results in my 308 bolt gun. I will shoot all fifty (50) loaded round over a chronograph, my old Oehler 35P and note the results, also before loading I will measure the case neck thickness of all the rounds.

Being retired and like many retired people I obviously have a surplus of time on my hands. Anyone with good loading software like Quickload is welcome to run the posted data and see what you come up with as I would be curious.

Muddling through all the numbers the most important question remains, how much does any of this matter? The most uniform brass was the WCC 10 while on the other end was the LC 13. So how much will it really matter?

Ron
 
Chainsaw. said:
Higgite, can you give me an example of "significant"? Just trying to rap my head around all of this.
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Sorry, I can't quantify "significant". I've measured some fired case volumes but didn't measure the resized volumes for a comparison. But, it is significant enough that QL recommends using fired case volumes for QL calculations. Other ballistic programs may vary, I don't know.
 
higgite:
Sorry, I can't quantify "significant". I've measured some fired case volumes but didn't measure the resized volumes for a comparison. But, it is significant enough that QL recommends using fired case volumes for QL calculations. Other ballistic programs may vary, I don't know.
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That being the problem as in how much is significant? Where does it begin to matter and if shooting from the 200 or 1,000 yard lines how much does it really matter?

Ron
 
A perfect, recent example:

I have 168 usable pieces of .307 Winchester brass. It's all W-W head stamp. It all looks the same.

While weighing some "mystery bullets" to see what they were, I happened to glance over at some of that .307 brass. Since some of it came to me second-hand (possibly third-hand), I figured I'd toss a few cases across the scale to see how consistent they were.

Unexpected results prompted me to weigh every, single piece of brass that I had.

68 pieces weighed 180 grains (decapped).
100 pieces weighed 160 grains (decapped).

At that point, it became obvious to me that these cases likely had different case wall thicknesses and different case capacities. Since .307 Winchester is operating right at the edge of safe and sane in Marlin 336 rifles (which is what mine was built from), differing case capacities can be a safety issue - not just a performance issue.

I seated spent primers in a selection of sized and trimmed cases and checked H2O overflow capacity.

The light ones had 58.0 gr H2O capacity.
The heavier ones had 54.0 gr H2O capacity.
That's a 7.5% difference - or, with some load data, more than the difference between a starting load and a max load.

If I had worked up a load in the 58 gr capacity brass and then loaded it in the 54 gr capacity brass, the load likely would have jumped well over max, instantly.
I even ran such a scenario through QuickLoad with a dozen different powders: The 'safe' loads in 58 gr capacity cases were kept at 49k-50k psi (max is cited as 51,000 or 52,000 psi, depending upon the source).
When I changed case capacity to 54 gr and modified no other variable, peak chamber pressure jumped to a minimum of 56k psi and most loads were well over 62k psi.

Is such an error likely to kill me instantly? No. It probably won't even pop the action.
But repeated use WILL damage the receiver.
(Marlin 336-family receivers stretch longitudinally when over-stressed, constantly increasing headspace and altering bolt lock-up [eventually popping the lever open with each shot], until they reach the breaking point and split the receiver.)
...And that's not even addressing the fact that muzzle velocity would be changing enough to substantially alter performance.


*Interesting note:
Some digging on .308 Winchester brass lead me to many charts like the one shown above by Reloadron.
The 'light' .307 Win cases align with standard 'commercial' Winchester .308 ammo, plus a few grains for the larger rim.
The 'heavier' .307 Win cases align with Winchester military/NATO cases (such as WCC), plus a few grains for the larger rim.
.307 Win was initially designed with thicker case walls, much like the WCC brass. But, based on more digging and known ages of some of this brass, I have come to the conclusion that Olin (Winchester) had to have some new drawing dies made at some point and they either: A) Forgot that it was supposed to have thicker case walls and just went with ".308 with a rim". Or, B) Wanted to save on raw materials, and decided the thicker case walls were not necessary.
Either way, loads worked up in 'new' brass would be dangerous in older brass.
 
Unexpected results prompted me to weigh every, single piece of brass that I had.

68 pieces weighed 180 grains (decapped).
100 pieces weighed 160 grains (decapped).
Click to expand...

Wow, just plain wow as I never would have dreamed such a spread could exist, 20 grains is a good chunk and reflects in the water capacity difference. Thanks for posting that as like I mentioned, I never would have expected that large of a delta.

Thanks
Ron
 
I will have to start a note book, but having weighted a fair amount of 30-06 and 308 brass from W, RP, Lapua, PPU, FC Hornady, Nossler.

I found a range of maybe 5 grains in any given head stamp. In caliber, 30-06 in FC ran up around 205 gr average and Hornady ran down around 180.

Clearly there would be some possible issues with max loads, but I don't think there is any question that Horrnady (and Nossler also on the light end) are not safe.

Per the .307, I would be questioning if I saw that range in the same mfg brass.

As for capacity, if its lighter it has to be thinner. Not unsafe in modern brass.

But how much difference does it take in capacity to be any issue?

Unclenick has posted some comparisons as I recall that said about zilch. Ratio of powder weight to water weight makes powder variance hugely less than water would appear to. Density.

As for not using distilled and soap, max nix, as long as the comparison is kept the same the relevancy is the same.

When we go to powder its not the same as water either and this is an attempt to compare the two.
 
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I loaded 250 30/06 cases with 5 different head stamps, the spread between the heaves and lightest was 27 grains.

F. Guffey
 
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