Rifle Brass Sorting Experiment - Part One

[Bindi2]

That's all hunky dory when your on good primers (most are). Best also hope you never get a mediocre or bad Lot (occasionally show up).
While they may very well not hurt your score by much, you likely won't shoot your best on a mediocre Lot of primers either.
And a bad Lot, can leave you "soul searching", and in wrong directions - IME

I use Federal 210s and have never seen a bad lot or variable lot across my hunting and range rifles with one exception they would not ignite AR2225/Retumbo satisfactory so I used 215s/Match 210s not quite single digit but that close It will do. There is one brand that is causing problems even after changing the firing pin spring which sorts most problems with primers/ignition. Either the cleaning when changing or the spring has lost tension in most cases. Surprising how many shooters wont have it that the spring is the problem. After the second or third stretch the marbles drop.

 

[Ammolytics]

FWIW: Weight sorting primers is one of the next things on my radar. That and testing the OBT theory w/ some strain gauges and oscilloscope. Stay tuned!

 

[JFrank]

Very informative fellas, I really appreciate anyone who takes their time and resources to test and post their results.
I also struggle with understanding where all the time comes from to do all these tests.
For me I always have to earn a darn living, not to mention a honey do list a 1/4 mile long to accomplish.
So when I read a simple way to go about something it really helps.

Thanks again fellas
Jim

 

[Depart123]

I don't know how anyone can accurately measure volume, when to my mind, the only volume that counts is as the case is fired and under pressure. The fired cases are going to rebound to slightly differing degrees, and sized cases pose the same problem.

But it would seem to me that as long as all the brass is of the same make and lot, the total weight of that brass then, represents the total amount of something other than powder and bullet in the chamber at the time of firing. (The primer not counting in this respect because it resides within a recess and therefore doesn't take up any volume).

That leaves only the primer ignition characteristics, and slight variations in bullet characteristics responsible for velocity differences.

Now, I'm sure I'll get some detractors. I'm certainly not a physicist, or an engineer, so where do these assumptions go wrong?

 

[dnellans]

I don't know how anyone can accurately measure volume, when to my mind, the only volume that counts is as the case is fired and under pressure. The fired cases are going to rebound to slightly differing degrees, and sized cases pose the same problem.

But it would seem to me that as long as all the brass is of the same make and lot, the total weight of that brass then, represents the total amount of something other than powder and bullet in the chamber at the time of firing. (The primer not counting in this respect because it resides within a recess and therefore doesn't take up any volume).

That leaves only the primer ignition characteristics, and slight variations in bullet characteristics responsible for velocity differences.

Now, I'm sure I'll get some detractors. I'm certainly not a physicist, or an engineer, so where do these assumptions go wrong?

The chamber volumetric argument is one I haven't heard before, but is an interesting question. If you have two cases that show the same internal volume, but different weights, presumably they are either different sizes externally, or the material is a different density. If they're -exactly- the same external dimensions, the only the density could differ. Hard to measure this without melting them down into an ingot

 

[dskogman]

The case volume vs weight is geometry dependent. Wall thickness of the case has a much bigger effect on volume than a thicker case head. The overall weight is a good approximation of the volume but when you get down to small differences is not so good.

 

[dmoran]

Below is a pair of .243-Win spent cases from one Lot of Winchester brass that measured in external lengths and widths identically, and near equal in capacity, but had a fairly large weight indifference. Both cases precisely sectioned with a lathe, then each section measured & weighed:

Note: in the cutting of each section with the lathe, 0.052" of material was removed for each cut.

Like in most all brass cases, the weight variations came from the thickness indifference to each section, as well as case head indifference's to extractor cuts, and metal thickness indifference's of the webbing and primer pocket floor. While on the outside cases appear and measure very equally, but on the inside, internally is where variations can be more readily seen and measured.

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[Scott Harris]

Below is a pair of .243-Win spent cases from one Lot of Winchester brass that measured in external lengths and widths identically, and near equal in capacity, but had a fairly large weight indifference. Both cases precisely sectioned with a lathe, then each section measured & weighed:

Note: in the cutting of each section with the lathe, 0.052" of material was removed for each cut.

Like in most all brass cases, the weight variations came from the thickness indifference to each section, as well as case head indifference's to extractor cuts, and metal thickness indifference's of the webbing and primer pocket floor. While on the outside cases appear and measure very equally, but on the inside, internally is where variations can be more readily seen and measured.

Below is another picture of Case A & B and a few of the others that I had also sectioned, to thickness measure and evaluate (many years ago now).

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Donovan, great info thanks. Have you done the same for Lapua brass?

 

[Ned Ludd]

I don't know how anyone can accurately measure volume, when to my mind, the only volume that counts is as the case is fired and under pressure. The fired cases are going to rebound to slightly differing degrees, and sized cases pose the same problem.

But it would seem to me that as long as all the brass is of the same make and lot, the total weight of that brass then, represents the total amount of something other than powder and bullet in the chamber at the time of firing. (The primer not counting in this respect because it resides within a recess and therefore doesn't take up any volume).

That leaves only the primer ignition characteristics, and slight variations in bullet characteristics responsible for velocity differences.

Now, I'm sure I'll get some detractors. I'm certainly not a physicist, or an engineer, so where do these assumptions go wrong?

You are correct that it is the volume of the "pressure cell" at the exact time of firing (i.e. under pressure) that is critical. The pressure cell volume is the internal volume of the case as it has expanded to match the chamber dimensions. One can always make the argument that fired cases spring back differing amounts. However, in my hands, the measured external dimensions of fire-formed cases are extremely uniform, suggesting that variance in the amount of spring back is quite small. Donovan's external measurements of two cases prior to lathe dissection as shown above also support that conclusion, both cases being identical to .001" in several different regions. Nonetheless, variance in the amount of spring back between different cases may not be zero, as you noted.

In considering what effect spring back variance might have on measuring case volume of cases after they have been fired (i.e. not during firing at their maximum expansion), the most important factor would not be the total amount of spring back, it would be the variance in spring back between cases, as you noted. In other words, if all cases had an absolutely identical amount of spring back, then the measured volumes would all be perfectly proportional to their volumes in a fully expanded state (i.e. during firing), and spring back wouldn't be an issue.

The key here is that the total amount of spring back in fired cases represents a relatively small fraction of the total internal volume. For example, it is not uncommon to push the shoulder back no more than .001" to .002" during the re-sizing process. The case walls down to an area just above the webbing are also squeezed down during the re-sizing process. But again, we're talking about a few thousandths here, which is only a tiny fraction of the overall internal case dimensions/volume. The spring back of the brass should not be any larger with respect to its effect on internal volume than what is done to the case during the re-sizing process. In other words, it's a very tiny fraction of the total case volume. More importantly, only the difference in spring back between different cases, which is an even much smaller fraction of the total internal volume, would be important.

The bottom line is that your premise about the fully expanded state of the brass being the critical volume component, i.e. the pressure cell, is correct. However, in more practical terms, variance in the amount of spring back between cases represents such a small fraction of the total internal volume that it is not a limiting source of error when using the internal volume measurement of fired cases as a surrogate to the pressure cell volume for comparative and/or sorting purposes. It's not really possible for the average reloader to measure brass volume while it's under pressure fully expanded, so we make the assumption that spring back is not a limiting source of error and measure the next best thing - the internal volume of fired brass.

As precision shooters, we want to control as many variables as we possibly can. Consistency/uniformity is absolutely critical for good precision. In order to achieve that, it is important to identify and address the limiting sources of error first (i.e. the largest and most critical sources of error). Spending significant amounts of time and energy to resolve some extremely minor source of error is wasted effort toward improving precision as long as much larger and more critical sources of error exist. So most reloaders start by addressing the obvious things they can easily control to a very high degree, such as charge weight, neck tensions, etc. Nonetheless, even small sources of error can be cumulative, so once the largest potential sources of error have been addressed, many reloaders will then start to tackle the smaller ones. This is not wasted effort, especially for those shooters at the top of their game in disciplines that require the absolute best precision possible. In fact, when competing at that level, addressing the small sources of error is most often the difference between winning and not winning. So you find people doing things like sorting brass by volume or weight, sorting bullets, weighing primers, etc.

The real key to any of these approaches is first to define the goal. What, exactly, is any specific sorting or improvement step in the reloading process aimed at achieving? Once that question is answered, it then becomes critical to employ an approach that is actually capable of achieving the goal, which brings us right back to understanding limiting sources of error. In the example highlighted in this thread of sorting brass by weight as a surrogate to directly measuring case volume, it is obvious that there is a general trend that is used as the basis for this approach: case weight is generally inversely proportional to internal case volume. Ammolytics' data at the beginning of this thread, the graph I posted illustrating the effect on volume of sorting cases by weight, and Donovan's dissection of cases using a lathe all indicate the same thing, heavier cases as a general trend have smaller internal volume than do lighter cases.

So what are the caveats (i.e. limiting sources of error) in terms of using case weight as a surrogate to directly measuring case volume? The answer is that the relationship is not perfectly linear. There will always be a certain number of outliers; i.e. data points that do not lie directly on the best straight line through a scatter plot of case weight versus case volume. For practical purposes, the reasons for these outliers may not even matter. They exist, and therefore may limit the usefulness of this approach, depending on the specific goal of the reloader. I showed previously in this thread how dividing weight-sorted cases up into three distinct weight groups (light, medium, heavy) reduced the internal volume variance by as much as one third or more. So there is no doubt that weight-sorting can be used to improve the consistency of case volume, but it is not a perfect approach and has its limitations. Although I personally have been satisfied with that level of improvement in uniformity of case volume for F-Class shooting, there is clearly still room for further improvement/refinement. The best example of this is Bart's preliminary use of a brass weight-sorting process, followed by more rigorous testing and sorting by the actual velocity produced. Sorting brass by weight alone in Bart's case wasn't sufficient to meet his expectations, so he further refined the process to meet his goals. So the bottom line is that goal of any such step needs to be clearly defined, then a method chosen (or created) that can deliver the desired results within the limiting sources of error associated with that particular method.

 

[rammac]

After having read that study that I posted about (earlier in this conversation) I'm not all that concerned with volume. Noting that the study showed that case volume has about the same impact on group size as neck tension and that most often only bench rest shooters are interested in tuning neck tension, I don't see any value to anybody other than a competition bench rest shooter.

 

[mikecr]

There is more to this than "internal volume of the case as it has expanded to match the chamber dimensions". The initial volume, the chamber clearances, and the energy taken from pressure peak to expand cases to chamber dimensions comes into play heavily (with hunting capacity cartridges).

I'm sure some here have noticed a trend in reporting of fire formed & yet to be body sized cases leading to pressure problems. That is, peak pressure is higher with this, and so the load will need to be adjusted. That alone is a reason to put off powder development until cases are fire formed to stable.
Changing clearances, and expansion resistances affects pressure peak.

Initial volume represents initial confinement, and we all know that affects powder burn.

 

[Bindi2]

The dissection of cases shows the lack of correlation between weight and volume.

 

[pat fulghum]

@BartsBullets and all..

Thanks for sharing your process!!!

Here is a simple question....
Once the case is removed from chamber and the velocity is written on the case, how does it stay there?

If you tumble the case with walnut shells won't the sharpie marker be gone?

So how do you clean the cases without removing the sharpie marker?
Are you just cleaning the necks with steel wool, brushing the necks, and cleaning the primer pockets?

- pat

 

[BartsBullets]

@BartsBullets and all..

Thanks for sharing your process!!!

Here is a simple question....
Once the case is removed from chamber and the velocity is written on the case, how does it stay there?

If you tumble the case with walnut shells won't the sharpie marker be gone?

So how do you clean the cases without removing the sharpie marker?
Are you just cleaning the necks with steel wool, brushing the necks, and cleaning the primer pockets?

- pat

Not easily! I’ll mark it at least twice.

I don’t clean cases. I just brush my necks.

Bart

 

[Depart123]

Below is a pair of .243-Win spent cases from one Lot of Winchester brass that measured in external lengths and widths identically, and near equal in capacity, but had a fairly large weight indifference. Both cases precisely sectioned with a lathe, then each section measured & weighed:

Note: in the cutting of each section with the lathe, 0.052" of material was removed for each cut.

Like in most all brass cases, the weight variations came from the thickness indifference to each section, as well as case head indifference's to extractor cuts, and metal thickness indifference's of the webbing and primer pocket floor. While on the outside cases appear and measure very equally, but on the inside, internally is where variations can be more readily seen and measured.

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So basically, the shoulder and neck account for almost 80% of the difference in weight? How the hell does that happen?

 

[JFrank]

Not easily! I’ll mark it at least twice.

I don’t clean cases. I just brush my necks.

Bart

I thought I was the only fella who doesn’t clean cases

 

[Bindi2]

I thought I was the only fella who doesn’t clean cases

Naah there are many more of us.

 

[dmoran]

So basically, the shoulder and neck account for almost 80% of the difference in weight? How the hell does that happen?

Have no first hand experience of cases being drawn from brass, or to why there can be variations encumbered in doing so. Just know that there is or can be, and with some brands it's more apparent.


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Donovan, great info thanks. Have you done the same for Lapua brass?

I have dissected cases from 4 Lapua cartridges (220 Russian, 6mmBR, 243-Win, 300-WM) over the years. While it does seem Lapua has high standards, I wouldn't judge them perfect. It has also appeared to me the bigger/larger the case is, more variations are likely (no matter what brand).

 

[Bindi2]

It is the method of production from a flat disc to a finished case. Depending on how many operations to form the neck from the cylinder pushes brass downwards, tie in annealing or lack of all have an impact.

 

[T-shooter]

Not easily! I’ll mark it at least twice.

I don’t clean cases. I just brush my necks.

Bart

I've noticed that if you write on a case with a magic marker, then heat it, the marks are hard to remove with any solvents. What about using a metal marking engraving pen, the ones that vibrate?