Why sort cases by weight?

[Dusty Stevens]

@Dusty Stevens now I’ve gone and done it

You can come join my therapy class. I get people shooting for fun again.

 

[Scott Harris]

Using fully-prepped, fireformed brass, I flip the primer around backwards (cup down) to prevent water from getting through the flash hole and into the primer, which is not effective "case volume". Trimming cases to uniform length should be part of brass prep, or weighing cases isn't likely to help.

The bottom line on the correlation between case weight and case volume is that some shooters will never believe that such a relationship exists, regardless of how much corroborating data is put in front of them. On the other hand, there are some that may be convinced that the correlation is valid. One group will never weight sort, the other might consider doing it. I'm tired of trying to convince those that will never believe there is a strong linear correlation between case weight and case volume, no matter what evidence is presented, so I'm not inclined to provide any further supporting data than what I already have. If you want to see some actual data, just do a search.

Even much better, if you're open-minded and curious, test case weight versus case volume for yourself. Load up 10 to 15 cases from the same prep/Lot, fire them, then determine the water volume of each fired case. I personally find it easier to weigh each of the cases before priming/loading them, but if you go that route, you have to mark or somehow keep track of each case so the volume determined after firing goes with the correct case. Plot case weight versus case volume, and have your graphing program perform a linear regression (i.e. generate the "best straight line" equation from the scatter plot data). Then you can decide whether the response appears linear in your own hands.



Cc - the idea here is not that some cases are overweight or underweight, the idea is to sort cases by weight into subgroups that have more uniform internal volume. As I mentioned, the correlation is not perfect...in other words, not every single value in a case weight versus case volume plot will be spot on the best straight line. There will always be a few outliers. Nonetheless, if you sort your cases by weight into 3 groups, i.e. light/medium/heavy, I think you will find the internal volume within each of the weight-sorted groups has less variance than if you had done nothing at all. Simple. That's all you can really hope to accomplish when sorting cases by weight - make the internal volume of weight-sorted cases more uniform than those not sorted by any method at all. The good news is that sorting cases by weight is stupid-fast and easy, so why not do it, especially if you compete in a discipline such as F-Class, where large numbers of loaded/fired rounds per match are the norm?

With a new Lot of brass, I typically record the weight of at least 50 cases. You need a good analytical balance to do this. I'm not talking about graphing of case weight here, just visually inspecting the sample data set, which is not difficult with a list of 50 or so numbers. Go through the values carefully...find the Hi/Lo values (i.e. determine the range) and try to get a feel for the distribution of case weights within the range. At that point, you can pretty easily make choices on where to set your weight limits for each sort group. This really isn't rocket science, it's all about using some simple physics and allowing statistics to work in your favor, no different than any other sorting process used by reloaders.

Well said Greg,
Weight is definitely correlated to case volume. There are many tests proving this, including a large study by the U.S. Army. Want better ES/SDs? Get together with some buddies, buy a crap load of brass, weight sort it and distribute amongst yourselves.

 

[group therapy]

You can come join my therapy class. I get people shooting for fun again.

is that a pun, this thread was gettin kinda dusty to me

 

[rardoin]

View attachment 1144247

Look closely, you can see the ink on the paper inside the bullet holes.
Red was the lightest 5 cases in the box
Blue was the heaviest 5 cases in the box.
284 win/Norma brass/180 Berger hybirds/powder measured on FX120i/600 yards


CW

Clay, were these shot in an alternating or random fashion or were they shot one group then the other?

Robin

 

[GSS]

I'm still fairly new here but,,
I get the Impression this Question has been asked and this topic discussed once or twice before here...

I'll have to try using the search function of the site to see what thread has the record for most pages of discussion.

I'm just a service rifle shooter and I sort my cases by weight for 600 yards ammo only into 1.0 grain max spread lots. Primarily plain old Lake City with same year headstamp and same number of times fired.

For important matches I also trickle the powder charge and make sure they are all on within 0.1 grains. The Electronic scale i use doesn't go out to 0.09 display.

I have done a blind test or two with Non weight sorted cases ( Avg 3.0 gr max spread ) and progressive loaded ammo so no trickled up powder charges. Shooting from the ground with only a sling for support like is done in the matches some days either group of ammo can appear to be better or worse.

Service Rifle is more of a shooter marksmanship / skill game than an equipment game / reloading contest so any noted differences that I think i may or may not be actually seeing are probably all on me.

 

[Mulligan]

Clay, were these shot in an alternating or random fashion or were they shot one group then the other?

Robin

Round robin
CW

 

[dmoran]

^^^^+1.... the best/fairest way to test all scenario's !.!.!
(one and the same aim point, alternating shots between increments/aspects).

 

[Mulligan]

^^^^+1.... the best/fairest way to test all scenario's !.!.!
(one and the same aim point, alternating shots between increments/aspects).

Exactly!!
CW