You will not get any argument from me on that point.
Weighing Brass
- Thread starter Rick Ratzlaff
- Start date
I have about 2gr spread on 220 6.5-284 LAPUA cases. About 3gr on 120 338 LM cases.
maybe sometime I'll check this out . to say I'm a doubting Thomas is putting it mildly .
my brass was 3 times fired with neck size only to hold a new bullet . it was never annealed , full length resized , nor was it trimmed .the way it came out of the chamber is how I weighed it . it was fired with the same load . the brass was getting tight in the chamber so I figured it was fully expanded to my chamber . so why is the capacity less than 0.5 grain different and case weights vary about 5.0 grains different .
the OP's brass is already once fired , so now what's he to do ?
My Lapua 300WM brass (300 pieces) is from the 80's.
I boogered my reply earlier, where I said my spread was .5gr in volume, I actually meant .5 cc in measurable difference, even with less than a 1gr weight spread.
This topic here has so many misconceptions, that a lot of you BELIEVE what you say to be true without understanding the fundamentals of cartridges and their manufacture. How much VOLUME brass displaces has no correlation to the combustion chamber if that combustion chamber VOLUME varies. XBBR, you are wrong in that brass all weighing the same has the same volume, it simply isn't true.
Cases will often weigh different due to a draw that gave the case an eccentric wall thickness, even the best brass in the business has this happen.
I worked in the business making ADI cases in 7.62 and 5.56 cases. All brass discs are punched from the same sheet, then they are stamped/cupped for the first draw. At this point, they are weighed, air gauged to make sure none are off spec, then put in the drawing machine.
Our observations running the weighing show that even when ALL the cases start from the same disc and sheet, the weights vary, the end product may vary quite a bit, but, INTERNALLY they are essentially the same.
This is why comparing WEIGHT to VOLUME is futile.
Also, different drawing dies are very rarely the same and give a different internal shape, changing the volume which may or may not show up as a different volume.
All brass formed, no matter which drawing machine was used it's dumped in the same hopper, marked the same on the head and stamped with the same batch number. So, your guess is as good as mine on what the actual case volume may be.
We also noted, that certain machines would draw a much longer neck prior to the final forming, which is trimmed off, is this brass lighter? We don't know.
Anyway, you can all believe whatever you wish, it makes no difference to me.
I check my VOLUME, it's the only way to know for sure what you are dealing with, and this notion of having the case in a die or whatever to measure the volume, well, a fired case will show a miniscule difference if springback varied by .001"-.002", my burette wouldn't even measure the difference.
Cheers.
I boogered my reply earlier, where I said my spread was .5gr in volume, I actually meant .5 cc in measurable difference, even with less than a 1gr weight spread.
This topic here has so many misconceptions, that a lot of you BELIEVE what you say to be true without understanding the fundamentals of cartridges and their manufacture. How much VOLUME brass displaces has no correlation to the combustion chamber if that combustion chamber VOLUME varies. XBBR, you are wrong in that brass all weighing the same has the same volume, it simply isn't true.
Cases will often weigh different due to a draw that gave the case an eccentric wall thickness, even the best brass in the business has this happen.
I worked in the business making ADI cases in 7.62 and 5.56 cases. All brass discs are punched from the same sheet, then they are stamped/cupped for the first draw. At this point, they are weighed, air gauged to make sure none are off spec, then put in the drawing machine.
Our observations running the weighing show that even when ALL the cases start from the same disc and sheet, the weights vary, the end product may vary quite a bit, but, INTERNALLY they are essentially the same.
This is why comparing WEIGHT to VOLUME is futile.
Also, different drawing dies are very rarely the same and give a different internal shape, changing the volume which may or may not show up as a different volume.
All brass formed, no matter which drawing machine was used it's dumped in the same hopper, marked the same on the head and stamped with the same batch number. So, your guess is as good as mine on what the actual case volume may be.
We also noted, that certain machines would draw a much longer neck prior to the final forming, which is trimmed off, is this brass lighter? We don't know.
Anyway, you can all believe whatever you wish, it makes no difference to me.
I check my VOLUME, it's the only way to know for sure what you are dealing with, and this notion of having the case in a die or whatever to measure the volume, well, a fired case will show a miniscule difference if springback varied by .001"-.002", my burette wouldn't even measure the difference.
Cheers.
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Ned Ludd
Silver $$ Contributor
Case weight can also vary due to differences in the extractor groove. The extractor groove has no relationship to internal volume whatsoever, either static or expanded. This topic comes up often at shooting sites such as this. Inevitably, someone will post a graph of case weight versus volume involving hundreds of data points. The best that can usually be said from the many data sets I have seen posted is that there is a very weak correlation, really just a trend, between case weight and case volume. Heavier cases generally tend to have less internal volume. However, many of the data points lie so far off the trend line as to be completely useless for predicting (or sorting) case volume (and therefore pressure) from brass weight. If you sort brass by weight, you will likely end up with sets of cases that on average may have more consistent volume than if they were not sorted at all. But you will also likely have plenty of outliers within any set that are quite different than the rest. This has been demonstrated time and time again with very large data sets.
Having compared sample groups (N=10) of weight sorted Norma 6XC cases vs un weight sorted cases as well as primer weight sorted groups vs un weight sorted primer groups dozens and dozens and dozens of times I can tell you that I have found that the case weight sorted sample groups as well as the primer weight sorted sample groups ALWAYS produce a lower SD and ES. ALWAYS !
Stop worrying about whether there is a correlation between case weight and internal volume. Do the actual experimental work. That is where the juice is
Stop worrying about whether there is a correlation between case weight and internal volume. Do the actual experimental work. That is where the juice is
I had heard this brought up often. So often that it got boring.
So last year I took 100 cases (Winchester 30-06 - same lot) and measured the diameter of all the extractor grooves.
Then I then I subtracted the smallest from the largest - and measured the width of the groove - so I got the volume of a band of brass that would represent the worst case of weight variance caused by this "variable.
It is less than 1/2 of a grain.
It is under the noise.
So, maybe we can put this lame puppy to rest now.
Interesting read, seems we all have our minds made up one way or the other.
Does an ackley improved case have a larger volume after fire forming? of course it does, however it weighes the same after fire forming, just has a different shape. So one would assume that there would be small changes in volume from a FL resized case after fired in a chamber, do to expansion in the chamber.
From a weight point of view, seems that virgin or once fired shouldn't make a dif. in the amount of variation of the brass. Once it has been stretched and trimmed, the weights could be different even if they were close before and the weight to vol. ratios would be slightly different.
I haven't used the water vol. method but i think i will give it a try as it seems to make the most sense to me. I will shoot my just purchased .223s to fire form them into .223ai then neck size them then weigh them and see what the actual water vol. is justs for kix.
Then maybe i will have a better feel if it is worth the extra work
Does an ackley improved case have a larger volume after fire forming? of course it does, however it weighes the same after fire forming, just has a different shape. So one would assume that there would be small changes in volume from a FL resized case after fired in a chamber, do to expansion in the chamber.
From a weight point of view, seems that virgin or once fired shouldn't make a dif. in the amount of variation of the brass. Once it has been stretched and trimmed, the weights could be different even if they were close before and the weight to vol. ratios would be slightly different.
I haven't used the water vol. method but i think i will give it a try as it seems to make the most sense to me. I will shoot my just purchased .223s to fire form them into .223ai then neck size them then weigh them and see what the actual water vol. is justs for kix.
Then maybe i will have a better feel if it is worth the extra work
Gstaylorg – I would have to disagree with you on this one.
To the best of my knowledge, the idea that the weight difference is due to differences in the extractor groove comes from Donovan and he has only shown us data from a small number of samples.
The flip side is charts showing correlation between weight and volume with large number of samples generally have good (instead of poor as you stated) and not just a trend (as you stated). Here is one I did with Lapua .308 brass with R2 of 0.826.
Anybody who knows statistics knows that you get the best prediction with a large data set and an R2 of 0.826 is not “very weak correlation” and many of the data points does not lie so far off the tread line (as you said to be completely useless for predicting case volume).
The thing to understand when doing this is there will always be NOISE in a system like this because the differences we are measuring is relatively small and so there will be noise from the weighting, and volume measurements. One cannot and should not expect a perfect fit where all the points lies on the line and you get an R2 value of 1.00. In fact anyone that comes here with such a set of data should immediately be suspected of making up data.
Ned Ludd
Silver $$ Contributor
Jlow - the extractor groove is simply one place in the case where where weight can change without affecting internal volume, but it is not the only place. The data you show above are much better than most I have seen. In fact, I have seen more than a few data sets where the line was almost horizontal due to the outliers. In your data set above, there are still some data points far enough off the line that would represent the outliers I mentioned in the previous post. Some of these would likely put those specific cases in a different sort group depending on whether you sorted based on volume or weight, and where the sort cutoff were set because they would be off by about a full X-axis unit (for example - the four points at approximately 172.00 below the line. I'm not at all hacking on your data because as I stated, they're much better than most I've seen. I also agree with you that your correlation between case weight and case volume is much better than most I have seen. The real question is whether having a few volume outliers in a lot of weight-sorted brass would actually lead to a detectable decrease in precision. In other words, would some of those outlying cases be the shots where points were dropped that might mean the difference between winning and not winning? I suspect the answer to that might differ for different individuals.
My point for the discussion above was simply to point out to anyone that may not be familiar with the the practice of weighing/sorting brass that weighing cases is not a perfect way to assess volume. Because I believe the general trend between weight and case volume does hold true, I routinely sort cases using the weight method. Mainly because it is quick and much easier than sorting by volume, which I am not willing to spend the time to do on a regular basis. But I do it with the understanding that there are going to be outliers, some of which may be off by quite a bit. So for the purpose of this discussion, I thought it pertinent to point out some of the potential issues with using this approach to sort brass. However, as I also stated above, I do believe that cases sorted in this manner will be more consistent in terms of volume than cases not sorted at all. How consistent will depend, in part, on how many outliers there happen to be in that particular lot of cases. It also likely depends on the accuracy to which volume was determined when data such as yours are presented. Weighing cases accurately on a balance is simple, whereas volume determination requires a bit more attention. It's not my intention to sway readers one way or the other regarding this sorting method, just point out the inherent sources of error so that others can make an informed decision of whether it is worth their time to do it.
As far as the extractor groove not accounting for weight/volume differences, that may well be true in some cases. However, even the data jlow presented above have some outliers. So there is something about the brass itself that leads to the weight method giving a less than optimal representation of volume for certain cases. Exactly what that "something" is can be debated, but it doesn't change the fact that it exists. The argument could certainly be made that accurate measurement of extractor grooves is not simple. The argument could also be made that the outliers were more likely due to errors in volume determination, such as a couple bubbles in the case, rather than weight determination. I'm not certain it is possible to address any of these questions in a way that will satisfy everyone, and I don't really care what method someone else uses. I have my approach and it has worked pretty well for me. However, I know something about sources of error and their effects on data interpretation and statements to the effect that certain things are written in stone are rarely true. Much of what we read here is opinion, nothing more. So in my opinion, discussions that might allow someone else to make a more informed decision are a good thing.
My point for the discussion above was simply to point out to anyone that may not be familiar with the the practice of weighing/sorting brass that weighing cases is not a perfect way to assess volume. Because I believe the general trend between weight and case volume does hold true, I routinely sort cases using the weight method. Mainly because it is quick and much easier than sorting by volume, which I am not willing to spend the time to do on a regular basis. But I do it with the understanding that there are going to be outliers, some of which may be off by quite a bit. So for the purpose of this discussion, I thought it pertinent to point out some of the potential issues with using this approach to sort brass. However, as I also stated above, I do believe that cases sorted in this manner will be more consistent in terms of volume than cases not sorted at all. How consistent will depend, in part, on how many outliers there happen to be in that particular lot of cases. It also likely depends on the accuracy to which volume was determined when data such as yours are presented. Weighing cases accurately on a balance is simple, whereas volume determination requires a bit more attention. It's not my intention to sway readers one way or the other regarding this sorting method, just point out the inherent sources of error so that others can make an informed decision of whether it is worth their time to do it.
As far as the extractor groove not accounting for weight/volume differences, that may well be true in some cases. However, even the data jlow presented above have some outliers. So there is something about the brass itself that leads to the weight method giving a less than optimal representation of volume for certain cases. Exactly what that "something" is can be debated, but it doesn't change the fact that it exists. The argument could certainly be made that accurate measurement of extractor grooves is not simple. The argument could also be made that the outliers were more likely due to errors in volume determination, such as a couple bubbles in the case, rather than weight determination. I'm not certain it is possible to address any of these questions in a way that will satisfy everyone, and I don't really care what method someone else uses. I have my approach and it has worked pretty well for me. However, I know something about sources of error and their effects on data interpretation and statements to the effect that certain things are written in stone are rarely true. Much of what we read here is opinion, nothing more. So in my opinion, discussions that might allow someone else to make a more informed decision are a good thing.
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dmoran
Donovan Moran
As could be said for your data as well.
Jpretle – I completely understand of it hurts your head. When I went to graduate school, statistics was my most hated subject… What I discovered though is at least in the scientific world where people don’t talk about that they think/feel but about what can be proven that I understand its role. I still don’t exactly love it but I use it as a tool.
Gstaylorg – My data does not necessarily discount contribution by the extractor groove but in order for us to take that into serious contention, a more robust study with significant number of cases of wide ranging weights needs to be done.
The lower quality of data you may have seen could be due to many things. For one thing, fired brass vs. new brass for the reasons I already mentioned – I myself have seen exactly the same thing first hand. Of course, there is also the skill of the tester and whether they QC their technique to verify that it is reproducible to the extent that they can see the small change in volume they are looking for.
You really cannot pick and choose my data to make your point – nothing personal but that is completely statistically invalid. It’s like if I pick and choose the ones that fall exactly on the line and tell you how perfect a fit I have…. The idea of running statistics is to avoid this type of bias. All data goes into the calculation of R2 and if that number comes up statistically significant, that is your answer. No ifs or buts….
ALL experimental data have outliers – that is the nature of the beast. For example, my results from these new unfired brass assumes that Lapua treated them exactly the same way but we know from our own experience that they don’t all come out the same when we measure headspace, neck thickness, etc and we have not talked about experimental error on my part which is always possible.
Your assumption is that these outliers are real, and they maybe. But there you are talking about perfection for every single round loaded and fired for a match, vs. whether weight is generally a function of the volume which is what we are talking about. I don’t think anyone assumes that weight is 100.00% predictive of volume. One can NEVER do this without a hell of a lot of testing. So from that standpoint, we are talking about apples and oranges.
I am actually surprised that you are now say that “the general trend between weight and case volume does hold true” as that would not be my conclusion reading your earlier post.
Dmoran – as for my data being suspect, that of course is always possible as you don’t know me. But if you assume that I am dishonest, then logically there is really no point in the discussion is there?
Gstaylorg – My data does not necessarily discount contribution by the extractor groove but in order for us to take that into serious contention, a more robust study with significant number of cases of wide ranging weights needs to be done.
The lower quality of data you may have seen could be due to many things. For one thing, fired brass vs. new brass for the reasons I already mentioned – I myself have seen exactly the same thing first hand. Of course, there is also the skill of the tester and whether they QC their technique to verify that it is reproducible to the extent that they can see the small change in volume they are looking for.
You really cannot pick and choose my data to make your point – nothing personal but that is completely statistically invalid. It’s like if I pick and choose the ones that fall exactly on the line and tell you how perfect a fit I have…. The idea of running statistics is to avoid this type of bias. All data goes into the calculation of R2 and if that number comes up statistically significant, that is your answer. No ifs or buts….
ALL experimental data have outliers – that is the nature of the beast. For example, my results from these new unfired brass assumes that Lapua treated them exactly the same way but we know from our own experience that they don’t all come out the same when we measure headspace, neck thickness, etc and we have not talked about experimental error on my part which is always possible.
Your assumption is that these outliers are real, and they maybe. But there you are talking about perfection for every single round loaded and fired for a match, vs. whether weight is generally a function of the volume which is what we are talking about. I don’t think anyone assumes that weight is 100.00% predictive of volume. One can NEVER do this without a hell of a lot of testing. So from that standpoint, we are talking about apples and oranges.
I am actually surprised that you are now say that “the general trend between weight and case volume does hold true” as that would not be my conclusion reading your earlier post.
Dmoran – as for my data being suspect, that of course is always possible as you don’t know me. But if you assume that I am dishonest, then logically there is really no point in the discussion is there?
Ned Ludd
Silver $$ Contributor
Reading discussions such as this thread is why I visit this site daily. As an old guy that started benchrest at 72 (reloading for 50+ yrs.), the variables that I ignored all these years, that others are discussing,makes a lot of sense. At times I wonder how I ever get good groups but have recently learned volumes on this site (still computer illiterate). I do have an excellent mentor for benchrest who keeps me on my toes.
I’ve no problem with you using my data. I’ve put it out there and so it is public.
The thing you should understand about why my data is better, it’s because handling small liquid volumes (micro liter) was a greater part of my job for more than 30 years in the laboratory and so it would be a surprise if I cannot get more reasonable data. The greater majority of the guys here who has tried this have basically zero experience dealing with small liquid volumes and so it again should not be a surprise that their data is rough. One cannot equate them.
This is why you have to take most of the data out there from people’s effort measuring volume with a big grain of salt. It’s like me laying bricks, I can certainly do it but compared to a master brick mason… So looking at the results of my brick laying as real data in terms of what it should actually look like is deceiving.
Sure outliers where weight does not relate to volume can potentially exist. It can exist because we have not tested ALL the possible variables that can cause volume variation, but at least in my hand, I have not seen any extreme outliers and I have not seen any convincing proof that other reasons are responsible.
We all do a certain type and degree of QC for our cases. The type and degree depend on our skills and the level of perfection desired in the final result. For the type of tactical shooting I do, what I do is perfect. If you are shooting long range BR, perhaps that is not enough and if you have the time and desire to measure case volume for each case, I have never thought that there was any problem with that.
dcali
Bullet Maker
Just to add a little perspective, the debate on the best way to measure case volume is generally not going to be useful when trying to get a hunting rifle under 1 MOA. All you can do there is buy high quality bullets, use a single lot of decent brass, measure carefully, and hope for the best. All this detail is for benchrest.
This is very true. We unfortunately frequently have discussions ONLY from our own point of perspective and frequently with no regard for other people who are more or less advanced that we are. This is also why there is frequently confusion/disagreement i.e. we are talking only about the same thing from a very general perspective but unfortunately with reloading, it’s the details that matters.
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