Questions about Weight-Sorting Cases

[South Pender]

I'm prepping new cases for my 6.5x55 and have chamfered the flashholes, trimmed them to the same length, and neck-turned them. These are Lapua cases, and I weighed 40 and found them all to be within about 1 gr. in weight--from a low of 176.8 gr. to a high of 177.9. I thought I'd sort them into two groups--the lightest 20 and the heaviest 20. If I do it this way, the weight variation in each group of 20 will be about .5 gr.

Here are my question:

1. Is this sorting worth the effort? To be sure, it didn't take much time, but if I passed on the sorting I'd have cases varying by up to 1 gr. in weight in groups shot.

2. In my two groups of 20 cases--with the variation in each of the two groups of 20 cases running .5 gr.--is this sufficient closeness in case weight for you guys shooting competitively? That is, in any group of 5 shot, the maximum case weight variation would be .5 gr., and in some groups shot, it would be less than that.

 

[Don Shelton]

I think sorting by volume is a better way. I’m not sure if any of it helps on paper,but I do a lot of case prep and am a little anal about little things.

 

[Jager]

A lot of guys weight-sort brass. A lot of guys don't.

The premise, as Don suggests, is that weighing brass is a simple, quick way to figure out volume differences. A premise that many of us feel has never been proven with any consistency.

What you might do is take that light batch and actually measure the volume in, say, five cases. Then do that for the heavy batch.

If you see a correlation between weight and volume, there's your answer. And if you don't, there's your other answer.

 

[M-61]

I'm prepping new cases for my 6.5x55 and have chamfered the flashholes,

Other than checking for burrs I would not touch the flash holes.

 

[South Pender]

Other than checking for burrs I would not touch the flash holes.

Yeah, the tool I used is an inside deburring tool

 

[Webster]

I'm prepping new cases for my 6.5x55 and have chamfered the flashholes, trimmed them to the same length, and neck-turned them. These are Lapua cases, and I weighed 40 and found them all to be within about 1 gr. in weight--from a low of 176.8 gr. to a high of 177.9. I thought I'd sort them into two groups--the lightest 20 and the heaviest 20. If I do it this way, the weight variation in each group of 20 will be about .5 gr.

Here are my question:

1. Is this sorting worth the effort? To be sure, it didn't take much time, but if I passed on the sorting I'd have cases varying by up to 1 gr. in weight in groups shot.

2. In my two groups of 20 cases--with the variation in each of the two groups of 20 cases running .5 gr.--is this sufficient closeness in case weight for you guys shooting competitively? That is, in any group of 5 shot, the maximum case weight variation would be .5 gr., and in some groups shot, it would be less than that.

while back someone pit a graph up on the website plotting wt VS volume. No correlation. Will try to find the graph.

 

[Webster]

I'm prepping new cases for my 6.5x55 and have chamfered the flashholes, trimmed them to the same length, and neck-turned them. These are Lapua cases, and I weighed 40 and found them all to be within about 1 gr. in weight--from a low of 176.8 gr. to a high of 177.9. I thought I'd sort them into two groups--the lightest 20 and the heaviest 20. If I do it this way, the weight variation in each group of 20 will be about .5 gr.

Here are my question:

1. Is this sorting worth the effort? To be sure, it didn't take much time, but if I passed on the sorting I'd have cases varying by up to 1 gr. in weight in groups shot.

2. In my two groups of 20 cases--with the variation in each of the two groups of 20 cases running .5 gr.--is this sufficient closeness in case weight for you guys shooting competitively? That is, in any group of 5 shot, the maximum case weight variation would be .5 gr., and in some groups shot, it would be less than that.

Ron Blane data 23 Jun 2017


Make whatever you want from the data.

 

[South Pender]

while back someone pit a graph up on the website plotting wt VS volume. No correlation. Will try to find the graph.

Wow. That's really hard to believe. I wouldn't expect a perfect negative correlation of -1.0, but I'd certainly expect a strong negative correlation--maybe something on the order of -.80. It's hard to imagine how it could be any other way.

Edit. I typed the above before seeing the data. After seeing the data, I computed the Pearson correlation coefficient between (a) empty case weight in grains and (b) case volume in cc. for the 10 LC13 cases. The Pearson correlation coefficient is -.80, just as one would expect.

Next, I did the same calculation for the WCC 10 cases and got a Pearson correlation coefficient of -.795.

I didn't take the time to do the computations for the other brands of cases, but the results for them should be fairly similar.

 

[South Pender]

Perhaps I can re frame the question. For you guys who do weight-sort your cases, would you consider a case weight variation of .5 gr. in a set of five you shot for group (say 6.5x55 cases weighing on average 177 gr.) to be sufficiently close in weight to eliminate case volume as a variable?

 

[Mulligan]

That is less than 1/3 of 1% variation in weight.
Be curious to see what others have to say.
CW

 

[BuffaloBill]

To measure volume I assume water is used, correct? The few times I’ve done that, I wasn’t sure how to best be consistent from one to the next, regarding surface tension; how high the water domes, etc. What advice does everyone have for me on that detail?

 

[BJung]

I own a M96 Target rifle and weight sorted Lapua brass two decades ago. I deburred the primer holes as well. I used 142 SMK with ( I think ) H4831. The groups were very group. That said, I can't say weighing brass made a difference because I never shot a comparison test load using brass of varying weights. I recently weight separated resized LC 30-06 brass to 7.7x58 brass, fireformed and trimmed to length. I then weighed volume weighed rubbing alcohol in each case. Case weight doesn't correspond to the same volume.

 

[Jeff Porter]

Praslick and Litz had a podcast about No BS BC and indicated that the weight variation in the brass is more due to variations in the cutting of the extraction groove than internal volume when formed the way Lapua makes brass.

 

[dannyjbiggs]

Perhaps I can re frame the question. For you guys who do weight-sort your cases, would you consider a case weight variation of .5 gr. in a set of five you shot for group (say 6.5x55 cases weighing on average 177 gr.) to be sufficiently close in weight to eliminate case volume as a variable?

Who knows!? I do it because I do it. And, in the past, I've sorted to the nearest grain, and to the nearest .5 grain. It generally depends on the quantity of brass that I am weight sorting, in order to come up with meaningful weight sorted batches. Awhile back, a friend and I went in together and purchased a 2,000 quantity of Lapua 6.5-.284 cases. Since I had a cold case of beer ready for the task, I agreed to weight sort the cases and share 50-50 with my friend. To make it fair, I came up with a recommended split and offered him first choice: High side or low side. Anyway, turned out I was able to sort to the nearest .1 grain. The smallest weight sorted batch on my "low side" share amounts to 132 cases (a 5x1000 match) at 193.2 grains average weight (Lot # 193.2 Lapua Shehane). Does it make any difference on paper? Who knows! Do I feel good about it? Immensely! My extraction grouves are more consistent.

 

[JEFFPPC]

Who knows!? I do it because I do it. And, in the past, I've sorted to the nearest grain, and to the nearest .5 grain. It generally depends on the quantity of brass that I am weight sorting, in order to come up with meaningful weight sorted batches. Awhile back, a friend and I went in together and purchased a 2,000 quantity of Lapua 6.5-.284 cases. Since I had a cold case of beer ready for the task, I agreed to weight sort the cases and share 50-50 with my friend. To make it fair, I came up with a recommended split and offered him first choice: High side or low side. Anyway, turned out I was able to sort to the nearest .1 grain. The smallest weight sorted batch on my "low side" share amounts to 132 cases (a 5x1000 match) at 193.2 grains average weight (Lot # 193.2 Lapua Shehane). Does it make any difference on paper? Who knows! Do I feel good about it? Immensely! My extraction grouves are more consistent!

That's only because you lived them with beer when cutting them. That's cheating!

 

[Don Shelton]

To measure volume I assume water is used, correct? The few times I’ve done that, I wasn’t sure how to best be consistent from one to the next, regarding surface tension; how high the water domes, etc. What advice does everyone have for me on that detaiActuallyBison Armory has a case volume die that uses air volume,check it out,,,works great

 

[6bra1k]

first it is another step in removing small variables.
the real question is can you and your rifle tell the diff ??
so what are you shooting ?
for my competition rifles i sort to the smallest practical.
plus or minus a tenth on my current adg 300 wsm brass over 100 pcs.
( you have to buy a lot and sell off what does not sort well)
i have actually done plus or minus 0.05...a half of a tenth.
there is no quality brass in the earlier charts.
the miniscus on the water surface can easily be brought to near flat by touch with a tissue to wick off small amounts.

 

[Rsadams]

For my accurate loads I weight sort brass and bullets and have seen improvement in my groups but it may be of course just all mental but if it makes me more confident so be it...

 

[Fuj]

For my accurate loads I weight sort brass and bullets and have seen improvement in my groups but it may be of course just all mental but if it makes me more confident so be it...

A lot can be said for the mental game. I also weight sort cases and
bullets. Winter was hard this year so it helps pass the time. Now I just
shot a .628" group at 500 yards and repeated with .871" group using
this method. I wonder if they would have been tighter if I weight sorted
my BR2's.....?? We'll save that argument for another day !!

 

[BuffaloBill]

Don,
The Bison Armory capacity die: https://bisonarmory.com/bison-armory-case-volume-gauge/

Very interesting! Looks like two pcbs each having a pressure sensor. Are they just measuring the air pressure inside the case, from the point where the case seals to the die surfaces on the upstroke? If so, how consistently can one case seal to the next? At the same height I mean, etc. Maybe I’m missing some important detail.