do you shoot 600 yard BENCHREST ???
Weighing internal case capacity
- Thread starter Reloader000
- Start date
No.
What does that have to do with the weight variance being mostly due to the variance in machining of the extractor groove ?
I didn't pull that out my *ss. The brass manufacturers say so.
Have you asked them if they shoot 600 yard BENCHREST ?
CharlieNC
Gold $$ Contributor
I weigh my brass and cull the obvious outliers to use as fouling shots. If the variability is "high" then I sort it into 2-3 tighter bins to shoot. Does it matter? It's so fast and easy to sort that I don't consider it worth the cost of testing so can't say for sure.
Ned Ludd
Silver $$ Contributor
I have measured case volume and weight for samples of every brass prep I've done for the last several years, then prepared graphs of case volume versus case weight. These analyses have covered a variety of different brands of brass (Lapua, Norma, Alpha, Starline, and PPU, to name a few) and three different cartridges (.223 Rem, .308 Win, .30-06). As assessed using a correlation coefficient, every single brass prep has shown a strong linear correlation between case volume and case weight, every single one. Other reloaders can argue all they want about the potential relationship between case weight and case volume, I've measured it, and it absolutely exists. I've posted many the graph demonstrating this principle over the years and if someone wants to look them up they are welcome to do so. This topic seems to come up so regularly that I have gotten tired of posting graphs supporting the notion that case volume is related to case weight over and over again.
As has been previously noted, once a case has been fired and expanded to fit the chamber, the extractor groove and the primer pocket are the only two places where case weight might vary without affecting case volume. For the obvious reason that we have to seat a primer in the processed case, differential primer pocket diameter is easy to assess. Primer pocket depth requires a measurement, but is also not difficult. For that reason, I can state with certainty that the primer pockets of the brands of brass I listed above are sufficiently uniform that they are not grossly affecting case volume/weight determinations. All I can say about the extractor groove dimensions is that if the width and depth were to vary sufficiently to affect case volume/weight determinations in a certain brand of brass that I haven't yet tried, I'd find another brand to use immediately. The extractor groove dimensions within a single Lot# appear quite uniform in the brands I have used.
If you want to try a relatively simple approach to improve your velocity stats, sorting cases by weight would be the first thing I would recommend. I would suggest starting by weighing 50 cases, recording the weight of each, and placing them in order in a reloading tray so you know the weight of each. Next, determine the overall weight range (extreme spread) so that you can divide the cases by weight into three distinct groups (light, medium, and heavy) that cover the entire case weight range. Once you have decided on the limits for each weight group, you have already weight-sorted 50 cases.
This approach is fast and simple and only requires a accurate/precise balance, which most reloaders already have for weighing powder. Using this approach will almost certainly reduce case volume variance within a certain weight group as compared to doing nothing at all, which is all most of us are really after in a sorting technique, right? We want a relatively simple method to improve consistency, and are not deluded into thinking we're making something "perfect"...just "better". The obvious caveat to this approach is that there can be outliers. In other words, if you make a graph of case volume versus case weight, not all points will lie directly on a straight line through the data scatter plot as shown here for some PPU 5.56 NATO brass:
Nonetheless, sorting this brass into light, medium, and heavy weight groups will still generally improve case volume consistency within each group as opposed to doing nothing at all. The reason for this is because of the strong linear correlation between case volume and case weight as evidenced by a correlation coefficient value (R) of almost 0.9 (a value of 1.0 would mean all data points were directly on the line). As I stated, we're not aiming for perfection, just an improvement. Sorting cases by weight as a surrogate for case volume is an easy way to achieve that goal. Here's the best news...sorting cases by weight will never make the case volume variance greater than it was before sorting. So all you really have to lose is a bit of time. There are certainly many other approaches aimed at obtaining more uniform velocity such as primer tests/sorting, uniforming primer pockets/flash holes, weighing powder to the half kernel, etc. All generally require significant time/effort as well as additional equipment (i.e. $$$). Sorting cases by weight is fast and easy and pretty much everyone in the reloading business already has some sort of weighing device. If not, there are some really inexpensive little balances available that would be suitable for weighing cases such as the Gem20.
As has been previously noted, once a case has been fired and expanded to fit the chamber, the extractor groove and the primer pocket are the only two places where case weight might vary without affecting case volume. For the obvious reason that we have to seat a primer in the processed case, differential primer pocket diameter is easy to assess. Primer pocket depth requires a measurement, but is also not difficult. For that reason, I can state with certainty that the primer pockets of the brands of brass I listed above are sufficiently uniform that they are not grossly affecting case volume/weight determinations. All I can say about the extractor groove dimensions is that if the width and depth were to vary sufficiently to affect case volume/weight determinations in a certain brand of brass that I haven't yet tried, I'd find another brand to use immediately. The extractor groove dimensions within a single Lot# appear quite uniform in the brands I have used.
If you want to try a relatively simple approach to improve your velocity stats, sorting cases by weight would be the first thing I would recommend. I would suggest starting by weighing 50 cases, recording the weight of each, and placing them in order in a reloading tray so you know the weight of each. Next, determine the overall weight range (extreme spread) so that you can divide the cases by weight into three distinct groups (light, medium, and heavy) that cover the entire case weight range. Once you have decided on the limits for each weight group, you have already weight-sorted 50 cases.
This approach is fast and simple and only requires a accurate/precise balance, which most reloaders already have for weighing powder. Using this approach will almost certainly reduce case volume variance within a certain weight group as compared to doing nothing at all, which is all most of us are really after in a sorting technique, right? We want a relatively simple method to improve consistency, and are not deluded into thinking we're making something "perfect"...just "better". The obvious caveat to this approach is that there can be outliers. In other words, if you make a graph of case volume versus case weight, not all points will lie directly on a straight line through the data scatter plot as shown here for some PPU 5.56 NATO brass:
Nonetheless, sorting this brass into light, medium, and heavy weight groups will still generally improve case volume consistency within each group as opposed to doing nothing at all. The reason for this is because of the strong linear correlation between case volume and case weight as evidenced by a correlation coefficient value (R) of almost 0.9 (a value of 1.0 would mean all data points were directly on the line). As I stated, we're not aiming for perfection, just an improvement. Sorting cases by weight as a surrogate for case volume is an easy way to achieve that goal. Here's the best news...sorting cases by weight will never make the case volume variance greater than it was before sorting. So all you really have to lose is a bit of time. There are certainly many other approaches aimed at obtaining more uniform velocity such as primer tests/sorting, uniforming primer pockets/flash holes, weighing powder to the half kernel, etc. All generally require significant time/effort as well as additional equipment (i.e. $$$). Sorting cases by weight is fast and easy and pretty much everyone in the reloading business already has some sort of weighing device. If not, there are some really inexpensive little balances available that would be suitable for weighing cases such as the Gem20.
I see the difference of the groups but where is your point of aim shown? (Likely off the page, correct?)
Dave
Mulligan
Silver $$ Contributor
Same point of aim, fired round robin with colored bullets at 600 yards.
CW
Before you conduct this type of study, I’d think that trimming all cases to the exact same length would be required (and not chamfering the inner or outside of the neck). Do you agree? And likely primer pocket uniforming would be helpful for this study as well before weighing brass, agree?I have measured case volume and weight for samples of every brass prep I've done for the last several years, then prepared graphs of case volume versus case weight. These analyses have covered a variety of different brands of brass (Lapua, Norma, Alpha, Starline, and PPU, to name a few) and three different cartridges (.223 Rem, .308 Win, .30-06). As assessed using a correlation coefficient, every single brass prep has shown a strong linear correlation between case volume and case weight, every single one. Other reloaders can argue all they want about the potential relationship between case weight and case volume, I've measured it, and it absolutely exists. I've posted many the graph demonstrating this principle over the years and if someone wants to look them up they are welcome to do so. This topic seems to come up so regularly that I have gotten tired of posting graphs supporting the notion that case volume is related to case weight over and over again.
As has been previously noted, once a case has been fired and expanded to fit the chamber, the extractor groove and the primer pocket are the only two places where case weight might vary without affecting case volume. For the obvious reason that we have to seat a primer in the processed case, differential primer pocket diameter is easy to assess. Primer pocket depth requires a measurement, but is also not difficult. For that reason, I can state with certainty that the primer pockets of the brands of brass I listed above are sufficiently uniform that they are not grossly affecting case volume/weight determinations. All I can say about the extractor groove dimensions is that if the width and depth were to vary sufficiently to affect case volume/weight determinations in a certain brand of brass that I haven't yet tried, I'd find another brand to use immediately. The extractor groove dimensions within a single Lot# appear quite uniform in the brands I have used.
If you want to try a relatively simple approach to improve your velocity stats, sorting cases by weight would be the first thing I would recommend. I would suggest starting by weighing 50 cases, recording the weight of each, and placing them in order in a reloading tray so you know the weight of each. Next, determine the overall weight range (extreme spread) so that you can divide the cases by weight into three distinct groups (light, medium, and heavy) that cover the entire case weight range. Once you have decided on the limits for each weight group, you have already weight-sorted 50 cases.
This approach is fast and simple and only requires a accurate/precise balance, which most reloaders already have for weighing powder. Using this approach will almost certainly reduce case volume variance within a certain weight group as compared to doing nothing at all, which is all most of us are really after in a sorting technique, right? We want a relatively simple method to improve consistency, and are not deluded into thinking we're making something "perfect"...just "better". The obvious caveat to this approach is that there can be outliers. In other words, if you make a graph of case volume versus case weight, not all points will lie directly on a straight line through the data scatter plot as shown here for some PPU 5.56 NATO brass:
View attachment 1432312
Nonetheless, sorting this brass into light, medium, and heavy weight groups will still generally improve case volume consistency within each group as opposed to doing nothing at all. The reason for this is because of the strong linear correlation between case volume and case weight as evidenced by a correlation coefficient value (R) of almost 0.9 (a value of 1.0 would mean all data points were directly on the line). As I stated, we're not aiming for perfection, just an improvement. Sorting cases by weight as a surrogate for case volume is an easy way to achieve that goal. Here's the best news...sorting cases by weight will never make the case volume variance greater than it was before sorting. So all you really have to lose is a bit of time. There are certainly many other approaches aimed at obtaining more uniform velocity such as primer tests/sorting, uniforming primer pockets/flash holes, weighing powder to the half kernel, etc. All generally require significant time/effort as well as additional equipment (i.e. $$$). Sorting cases by weight is fast and easy and pretty much everyone in the reloading business already has some sort of weighing device. If not, there are some really inexpensive little balances available that would be suitable for weighing cases such as the Gem20.
Ned Ludd
Silver $$ Contributor
I trim/chamfer the cases every firing using a Giraud trimmer, which generates very uniform length and inside/outside chamfer. I think it is less critical that primer pocket depth be made uniform, as it seems to be pretty decent as is, at least in the brands I've been using. That's not to say there isn't a small amount of variance in primer pocket depth, there almost certainly is. However, it doesn't seem to involve a sufficient mass of brass to render the case volume versus case weight curve non-linear.
fired and trimmed
I used the the primer pocket plug from 21st century innovations .nope dint measure grove and primer pocket
Great tip’ thx I think I’ll order one soon.
Great question. I have no idea how to answer your question definitively. However, in my game when 1st and 10th place are separated by less that 4 points out of a 1,200 score I am willing to spend the time weight sorting and batching my brass. I wish I had a more definitive answer to know if I am wasting my time.
Mulligan
Silver $$ Contributor
The photo of the two groups below shows the difference of sorted Norma brass at 600 yards. Bullets were colored with sharpies, all rounds shot round-robin out of a 284 win F-open rifle.
I have found weight sorting different brands of brass yielded different results. YMMV.
Heavier brass prints higher most of the time..... in my tests at distance.
In regards to SD and ES
For me, I ignore it...... all of it. I personally am not convinced my labradar is accurate enough to look at the small samples and give reliable data. I can do math just fine, and my thesis a lifetime ago was statistics based I understand how to calculate the numbers and what they mean as well as anyone. Just because we can measure it with our limited tools, does not mean we can take the results to the bank. In the disciplines I participate in, I have never seen an award presented for either ES or SD. I know folks use these numbers to tune, I have tried and it has never worked for me, again YMMV.
Kind Regards
CW
I have found weight sorting different brands of brass yielded different results. YMMV.
Heavier brass prints higher most of the time..... in my tests at distance.
In regards to SD and ES
For me, I ignore it...... all of it. I personally am not convinced my labradar is accurate enough to look at the small samples and give reliable data. I can do math just fine, and my thesis a lifetime ago was statistics based I understand how to calculate the numbers and what they mean as well as anyone. Just because we can measure it with our limited tools, does not mean we can take the results to the bank. In the disciplines I participate in, I have never seen an award presented for either ES or SD. I know folks use these numbers to tune, I have tried and it has never worked for me, again YMMV.
Kind Regards
CW
tom
Gold $$ Contributor
Chasing the chronograph blindly will take you out of tune potentially. We tune by pressure, and although related, it's not a 1 for 1 ratio. Sorting that way isn't a bad idea though, or just tagging out oddballs during normal development. Guys that came before me used to cut right to the chase and sort by point of impact lol.
Volume is directly related, so worth the time for me now that it's easy. It makes it easier for cases not derived from lapua 6br brass lol.
Tom
Volume is directly related, so worth the time for me now that it's easy. It makes it easier for cases not derived from lapua 6br brass lol.
Tom
Ned Ludd
Silver $$ Contributor
The direct answer to your question would be no, but only if velocity remained fairly constant for cases of varying weight/volume, which isn't what usually happens. In my hands, the effect is most readily observed with .223 Rem brass, where everything seems to matter a little more than it does with larger cartridges. With Lapua .223 Rem brass, the heaviest cases tend to exhibit as much as 20-30 fps greater average velocity than the lightest. This is enough to potentially put the load out of tune.
In contrast, I do not observe the same [large] velocity variance between the heaviest and lightest cases in .308 Win or .30-06 cartridges. The velocity variance in those cases due to internal volume variance (i.e. case weight variance) is much smaller, often within, or less than the velocity SD for a given string of fire. So one could argue that the benefit of weight-sorting such larger cases is much less, or perhaps even non-existant, in comparison to a small case such as the .223 Rem, where the effect is readily quantifiable and significant. Nonetheless, the principle involved is the same, so I sort the larger cartridges as well. If nothing else, I figure it might help eliminate one or two fliers in a given match that could cost me points and be the difference between winning and not winning; i.e. minimizing outliers. But I can't prove that. I can only suggest that the notion of weight-sorting brass is consistent the effect we know case volume variance can have on velocity. There are some things in the reloading process that are difficult to prove definitively, and we sometimes have to do things we only believe might be of benefit.
The notion of sorting brass by weight is at all not about chasing the chronograph blindly, or at least, it shouldn't be, as Tom noted. It is simply about minimizing velocity variance due to case volume variance within a single weight sort group. Nothing more. It's just a fairly quick and simple method to improve case volume consistency. It isn't about achieving perfection and it certainly won't make a bad load shoot well. Nonetheless, for disciplines such as F-Class where long strings of fire are the norm (20+ shots), it can be a useful tool to help maintain more consistent velocity during the course of a string of fire.
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