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Acceptable brass weight and volume

alpha brass.jpg View attachment 1088345 there has not been a thread on this in awhile and I am curious as to what the current opinion is on brass weight and volume consistency. I currently do not sort and am not sure I would see much of a difference on paper if I did but am thinking of giving it a try. Also wondering how this Apha brass consistency stacks up against Lapua and Peterson brass consistency if anyone can answer that. I have used all three brands now and no complaints with any of them as far as quality in other aspects.

This is 3 times fired 6mm Creedmore . I weighed each case three times to make sure I was getting fairly accurate readings from my scale. A small sample but should be enough to show any trends
 
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Myself for a case of that capacity, 4-tenths or so would be my max target weight for segregations.
How well did the "wet weights" repeat?
 
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If you take two pieces of brass that have the exact same weight and internal volume to 4 decimal places, then crush one of the two pieces with a pair of pliers, what happens to their weight and volume? Brass external dimensions will affect internal volume without changing weight.

Certainly the manufacturer has a role in how uniform things are that markedly affect brass weight and internal volume, such as case wall thickness and extractor groove width. But the user also plays a role along the same line as my question above with regard to how uniform re-sized brass dimensions are. In my hands, most weighed case volumes will fall fairly close to the best fit straight line with respect to case volume (i.e. pretty decent correlation coefficient). However, there will always be some outliers. Presumably, these outliers are due to variance in the extractor groove, body diameter, shoulder bump, etc. Notice that at least two of those variables are as (or more) dependent on the reloader as the manufacturer, so there is always going to be a limit on how good the correlation between case weight and volume will be, regardless of the manufacturer.
 
@Ned Ludd ....
Looking at his data, his correlation is not very good.
Unlike you, myself typically do not see good correlation in weight/volume. More so the larger the capacity.
Just my 2-Cents
 
I'm strictly using .308 Win and .223 Rem cases, which do not have all that large a capacity. I also strictly use Lapua brass, so maybe there is something more to the manufacturer's contribution.

Without actually graphing out the OPs data brass weight versus volume above, I see that brass weight (10 cases) has an ES/SD of ~1.00 +/- .33 gr, and case volume has has an ES/SD of 0.77 +/- 0.51 gr. The density of brass is about 8.5 times greater than water, so clearly the case volume variance is much larger than the case weight variance, which goes directly to my point above, that anything that affects dimensional aspects of the case, whether at brass manufacturer's end, or in the hands of the reloader themselves, have the potential to generate outliers. If there is not a good correlation between case weight and case volume, then the safest approach is simply to sort cases based on actual water volume. I find that to be a PITA for the quantity of cases I use in competition, and probably not necessary for my chosen discipline (F-TR), so I usually sort by case weight. In my estimation, sorting cases solely by weight (rather than actual internal water volume) is much better than doing nothing at all, and relatively easy in terms of time and effort. Nonetheless, if I thought it really made a difference, I'd sort my cases by water volume.
 
There is no consistency, you can't reasonably predict volume by weighing the cases.

Actually, you can. The amount by which variance in the dimensions of different regions of the brass case itself affect internal volume are really quite small relative to the total internal volume. Some variance between case weight and volume is to be expected, but if it's really large, I suspect that other errors are in play, such as accurate determination of internal water volume, or the external dimensions of the cases themselves may simply not be uniform.
 
Quickload tells you to measure case capacity with cases fired in your chamber and not resized cases. You want the exact size of the fired case because this volume effects the chamber pressure and velocity.

"BUT" higher quality cases like Peterson are weight sorted for uniformity. And its up to the shooter to check the case capacity for the type shooting they may be doing.
 
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Actually, you can. The amount by which variance in the dimensions of different regions of the brass case itself affect internal volume are really quite small relative to the total internal volume. Some variance between case weight and volume is to be expected, but if it's really large, I suspect that other errors are in play, such as accurate determination of internal water volume, or the external dimensions of the cases themselves may simply not be uniform.

Actually, no, you can't. Volume has a huge effect on everything that happens to the bullet. Ballisticians don't distinguish between where a case volume changes, they just want to know how much volume the case has. The chart I posted shows that there is no relationship between weight and volume, there is no reason to guess as to whether there is a relationship. Even with 10 data points you can see that as the weight increased the volume is random, it jumps all over the place. You can't say that if my case weight increases by a tenth of a grain then my volume will increase by X amount.
 
The extreme spread on the dry weights was 1.0 gns the extreme spread on the filled cases was .77 gns is that good or bad ? BTW this is only the second time I have done this.I used a small ball of temporary adhesive putty (think blue plumbers putty) to fill the primer hole. I used the same ball for each case for conformity. Filled the cases with an eye dropper tilting the case and tapping for bubbles. Skimming themenicus with a plastic card and drying the case walls with a paper towel before weighing.

BTW I edited the original post because the first image of the database had some columns hidden and it was confusing, apologies
 
If 100 cases with the same volume have the same amount less if full into an FL sizing die making their outside perfectly round and uniform in size?

In other words, how much out of round do cases need to reduce their water capacity 1/10th grain?

It would depend on the shape and size of a granule of powder. I can tell you that mathematically it would only take about .0005" change in the radius of the case to create a volume difference of .027 square inches.

Ooops, I have to change that.

After double checking it looks like a .002" change in the shoulder diameter will create .001 cubic inches change in the case volume and .001 cubic inches change in volume will produce about 175 PSI change in max chamber pressure which changes the muzzle velocity by about 1 FPS (using IMR 4198 in a .308 case).
 
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The extreme spread on the dry weights was 1.0 gns the extreme spread on the filled cases was .77 gns is that good or bad ? BTW this is only the second time I have done this.I used a small ball of temporary adhesive putty (think blue plumbers putty) to fill the primer hole. I used the same ball for each case for conformity. Filled the cases with an eye dropper tilting the case and tapping for bubbles. Skimming themenicus with a plastic card and drying the case walls with a paper towel before weighing.

BTW I edited the original post because the first image of the database had some columns hidden and it was confusing, apologies

Without comparing the variation in case weights to volumes of several brands of cases you can't really tell. Your dataset is too small to really do a valid comparison but even if you had a 100 cases you'd still need to do the test over several brands before anyone can say whether this data is any better than another set of data.

Besides, as I've shown from your limited data, there isn't any correlation between weights and volumes so there is no valid way of proving whether this is good or bad.
 
I guess I wasn't clear as to what I am asking. I know ten samples is not a statistically significant number. I also know that dry weight does not correlate to volume.
I was just asking if anyone knew what the average deviations on Peterson, Norma and Lapua brass are normally. I was also wondering how many do sort their brass by volume and how much deviation did they allow for. I have 200 of these cases and was considering sorting out 75 or 100 for matches. No need to over analyze
 
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Below from the Peterson website, they have case weight and internal volume quality standards.

Quality Assurance

Stringent Testing, Maximum Quality
https://www.petersoncartridge.com/our-process/qa

Weight
The cartridge is weighed to verify manufacturing specifications.


Internal Volume
The internal volume of the cartridge is measured and verified.


Peterson Select
Weight and length sorted 50-count boxes.
https://www.petersoncartridge.com/products/peterson-select

Peterson Select casings are weight sorted at the factory.
All casings in a 50-count box are guaranteed to be within one grain of each other.
They are also sorted by overall length and guaranteed to be consistent to within .001 inch.
 
Thanks, that is the sort of info I want. I tried some Peterson in .260 last year. It was good brass but I ran it pretty hot and retired it with the barrel. I used to do strictly Lapua but I like to try new stuff and methods
 
After double checking it looks like a .002" change in the shoulder diameter will create .001 cubic inches change in the case volume and .001 cubic inches change in volume will produce about 175 PSI change in max chamber pressure which changes the muzzle velocity by about 1 FPS (using IMR 4198 in a .308 case).
What if the 308 case body, shoulder and neck is elliptical by .002"?
 
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After double checking it looks like a .002" change in the shoulder diameter will create .001 cubic inches change in the case volume and .001 cubic inches change in volume will produce about 175 PSI change in max chamber pressure which changes the muzzle velocity by about 1 FPS (using IMR 4198 in a .308 case).

sorry I missed this post but basically you are saying it would not change my velocities enough to make a darn. I found case volume weighing had the entertainment level of watching a Lifetime movie with the wife and the mother in law so that is welcome news
 
Actually, no, you can't. Volume has a huge effect on everything that happens to the bullet. Ballisticians don't distinguish between where a case volume changes, they just want to know how much volume the case has. The chart I posted shows that there is no relationship between weight and volume, there is no reason to guess as to whether there is a relationship. Even with 10 data points you can see that as the weight increased the volume is random, it jumps all over the place. You can't say that if my case weight increases by a tenth of a grain then my volume will increase by X amount.

I'll try to explain in a coherent manner why I respectfully disagree with some of the claims in your statement.

Under the typical peak internal pressures of 50-60K psi that occur in centerfire cartridges, the brass case undergoes plastic deformation and adopts a conformation that closely matches the chamber in which it was fired. In fact, fired cases are generally extremely uniform in their external dimensions, often as uniform as in prepped (resized) brass. Because brass has a density of about 8.5 times greater than water, as the internal volume of a case increases, it's relative weight will decrease. This is simple physics. So what are the possible sources of error that could lead to the internal volume of cases NOT being proportional to their weight?

1) The first major assumption in using case weight as a surrogate method for estimating case volume is that the density of brass within a single Lot # of cases is uniform. If you do not believe the density of brass within a single Lot # is uniform, we can agree to disagree on everything else and there is little point in reading any further. I would not make such a claim for the density of brass from different Lot#s (or from different manufacturers). Comparing brass by weight from different Lot #s, or different manufacturers, may be comparing apples to oranges.

2) If all external dimensions of two hollow objects are identical, and they are composed of material of identical density, then there WILL be a proportional relationship between their internal volumes and their weights. This is simple physics and not subject to "interpretation". So the main question becomes, what could be the cause any possible discrepancy in the exterior dimensions of two cases fired in the same chamber? There are two most likely possibilities:

A) The region around the bottom of the case that includes the primer pocket, the extractor groove, and various other beveled surfaces, is the part of the case that DOES NOT expand to closely fit the external dimensions of the chamber. Some of these dimensions, such as casehead diameter may differ slightly, and to some extent do undergo deformation under sufficient pressure. However, they can effectively be removed from consideration by the simple physical constraints they are subject to. For example, If the diameter of the casehead grows too large, it will cause difficulty in chambering that case. Along the same line, if the diameter of the primer pocket itself is too large, or too small, primers will not fit properly. Further, significant changes in the depth of the primer pocket would also be obvious, because a uniforming tool would only work in some cases, but not others. So in general, we have a number of simple observations that allow us to conclude whether the outer dimensions of the casehead and primer pocket regions of the brass have been significantly altered.

The obvious remaining culprit in this region of the case is the extractor groove. Certainly, non-uniformity in the extractor groove dimensions between two cases with otherwise identical external dimensions would directly cause a change in case weight without affecting case volume. In fact, I do believe that variance in dimensions of the extractor groove is likely to be at least part of the reason for the existence of "outliers", where case volume lies off the trend line for case weight versus case volume. I have examined the extractor grooves on many a case from a single Lot # and I can tell you simply by eye that whatever variance there may be between cases, it is equivalent to only a very small fraction of the total internal volume of the case. Therefore, there would need to be a large relative difference in the size of the extractor grooves of two cases to account for any significant variance between their case weight to case volume ratios. Nonetheless, I acknowledge that this is a likely source of the observed variance between the two values.

B) The second most obvious way in which the outer dimensions of two cases that were fired in the same chamber could differ significantly would be some sort of stress or damage that occurred after the round was ejected from the chamber. In fact, various types of damage such as flat-spotting of necks or dings to the shoulder are quite common with strong ejector springs. Anything that changes external dimensions of a case without altering the mass of brass in it will cause it to move off a trend line for a graph of case weight versus case volume. Squeezing a case with pliers as I mentioned in an earlier post would be an extreme example of this phenomena. The key here is that it is critical to closely examine cases for which you are determining case volume, whether directly with water, or by weight comparison, because changes in the external dimensions of the case will affect the outcome regardless of which approach you use. Simple quality control approaches for any cases that appear to be far off the trend line are simple visual inspection and/or direct measurement of case body, neck, shoulder, etc., external dimensions.

These are my arguments to support the notion that within reasonable limits, case weight should be proportional to case volume. As a demonstration that, in fact, empirical evidence also supports this notion, I have attached two examples of case weight versus case volume for two fairly recent brass preps in one of my rifles. Every time I start in with a new prep of virgin brass, I carry out this analysis. As a result, I have determined case weight and respective case volume for thousands of cases over the years, usually in small groups such as these. I'd much rather have a single data set for several hundred cases all determined at the same time, but frankly, I'm way too lazy to do that many all at once. These two files might be considered as representing approximately the best (top graph) and worst (bottom graph) case scenarios with respect to the trend lines I typically obtain from this kind of analysis. The top graph is about the best group of cases I have ever seen, the bottom is a little worse (more outliers) than average. Both are relatively small numbers of cases from a statistical point of view (n=10, n=15). There are some minor differences such as the use of different units for the x- and y-axes, which do not effectively alter the relative trend lines in terms of regression analysis. Nonetheless, there are two critical take-home messages from these graphs. The first is that in both cases, the trend line shows a clear negative slope, meaning that as case weight decreases, case volume increases. The second is that the coefficients of correlation (r) are both positive, and much closer to 1.0 than zero. Thus, regression analysis also supports a strong linear association between the x and y variables (case weight and case volume).

I have spent the better part of my adult life in a laboratory, routinely measuring and analyzing extremely small quantities of liquids and solids. I know something about what it takes to do this properly, and with good precision. My gut feeling is that in many cases, people having difficulty quantifying case volume with water are either using measuring equipment that is not appropriate, or their technique is lacking. For example, it is very easy to leave a bubble inside the case, which will cause a significant error in the determined water volume. In addition to the variance in case weight that should be independent of case volume (i.e. variance in the extractor groove), I also believe that error in water volume determination may be part of the reason why not everyone that compares case weight to case volume observes trend lines such as I illustrated here. As I mentioned above, I have routinely carried out this simple analysis with almost every single prep of virgin brass I have done over the years. I have yet to observe a single occasion in which there was not a clear negatively sloped trend line for a graph of case weight versus case volume.

For what it is worth, I do not use the case weight and trend line equation to "estimate" case volume from such a graph. It is simply part of the characterization process for a new brass prep. Because of the existence of occasional outliers that clearly are well away from the trend line, I believe trying to estimate case weight from the graph is not a useful endeavor. As I stated in an earlier post, I use measured case weight as a relatively simple approach to improve consistency of case volume, without having to actually determine case volume with water, which I find to be somewhat of a PITA. I use case weight to sort cases into sub-groups, which I believe are more uniform with respect to volume than if I had done nothing at all. That is my only claim. My arguments as to why this is a valid approach, and data supporting those arguments is presented above. As always, YMMV.






C-V 95 SMK Brass Analysis.jpg


C-V Case Wt vs Vol 2-01-17.jpg
 
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Ned, your graph shows the heavier weight cases seems to percentage wise have less case volume so when load batching would starting with the heaviest case weight and loading with the heaviest bullet working from heaviest weight to lightest for both cases and bullets that are closely batched together help even out the es for long range.
 

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