Jcalhoun, I appreciate your post as many precision shooters weight their cases for the reasons you've elaborated. However, I do not share your views as regards the benefits of this practice.
I believe that weighting cases on the assumption that there is a constant correlation between case weight and internal volume is a complete waste of time that is based on an erroneous assumption. Others factors such as dimension of base and extractor groove are significant confounding variables.
With new brass, I expand necks to uniform size, turn them for uniform thickness, trim to uniform length, chamfer, clean primer pockets and deburr primer holes. After fireforming, I routinely measure internal volume of 30 cases in order to adjust Quickload parameters to customize it my firearm. I have done hundreds of these measurements and I have found that even with the best of brass (Lapua), the correlation between case weight and internal volume is extremely weak and typically less than 50% valid.
Nothing like a little data to illustrate the point. Here's a sample of 30 fireformed Remington cases in my 338 Edge. All cases have been prepped as described above. The empty and water-filled cases were weighted on an Acculab VIC 303 that is accurate within .001 gram or .02 grain. A drop of dishwashing soap was mixed with the water used for the tests to reduce surface tension and ensure consistency from case to case.
#.....Case weight (grs)……Var. %……..Water weight (grs)….Var. %
1…….272.68……………………-1.19%.............116.66…………….-0.04%
2…….276.74……………………+0.28%............117.00………… ….+0 .25%
3…….272.68……………………-1.19%.............117.10…………….+0.34%
4…….267.24……………………-3.16%.............117.48…………….+0.66%
5…….278.84……………………+1.04%............116.18………… ….-0.45%
6…….276.24……………………+0.10%............116.62………… ….-0.07%
7…….278.14……………………+0.79%............116.12………… ….-0.50%
8…….276.22……………………+0.09%............116.56………… ….-0.13%
9…….280.58……………………+1.67%............116.24………… ….-0.40%
10…..276.48……………………+0.19%............116.40………… ….-0.26%
11…..276.58……………………+0.22%............116.50………… ….-0.18%
12…..276.76……………………+0.29%............116.64………… ….-0.06%
13…..279.64……………………+1.33%............116.64………… ….-0.06%
14…..278.16……………………+0.80%............116.80………… …+0 .08%
15…..277.18……………………+0.44%............116.78………… …+0 .06%
16…..277.60……………………+0.59%............116.64………… ….-0.06%
17…..275.82……………………-0.05%.............116.82……………+0.10%
18…..271.74……………………-1.53%.............117.20……………+0.42%
19…..276.40……………………+0.16%............116.72………… …+0 .01%
20…..271.68……………………-1.55%.............116.86……………+0.13%
21…..275.62……………………-0.12%.............116.94……………+0.20%
22…..276.32……………………+0.13%............117.22………… …+0 .44%
23…..276.00……………………+0.01%............116.96………… ... .+0.22%
24…..278.02……………………+0.75%............116.74………… …+0 .03%
25…..273.90……………………-0.75%.............116.54…………….-0.14%
26…..278.00…………………..+0.74%............116.52……… …….-0.16%
27…..275.60……………………-0.13%.............116.10…………….-0.52%
28…..276.62……………………+0.24%............116.74………… …+0 .03%
29…..275.44……………………-0.19%.............116.74……………+0.03%
30…..275.94……………………-0.01%.............116.72……………+0.01%
Ave..275.96………………………..…………………....116.71
Using the 0.5% variation standard normally advocated (+ or - 0.25% from average), one would have selected 13 of the 30 weighted cases. Selecting by internal volume would have resulted in 20 retained cases. Moreover, 3 of the cases selected by weight would have been rejected by volume (#10, 22 and 27). Consequently, selecting by weight would have resulted in the identification of 10 of the 20 cases that had relatively uniform internal volume.
If one looks at the validity of the assumption of case weight as an indicator of internal volume within a 0.5% variation, it would appear that the assumption is dubious at best. For example, you would expect case #1 which weights 1.19% less than the average of 30 cases to have approximately 1.2% greater internal volume than the average volume for the same cases. Instead, that case is almost perfectly on the mark for case volume (-0.04%). Indeed the correlation is valid only for 11 of 30 cases (#6, 8, 10-12, 17, 19, 21, 23, 29 and 30) or 36.7%.
Another interesting observation from the table above, is that the weight variation among cases is quite large (-3.16% to + 1.67% = 4.83%), whereas the internal volume is relatively constant (+0.66% to -0.52% = 1.18%).
I and 2 of my shooting buddies have run this same experiment independently with hundreds of cases, using 5 different brands of brass (WW, RP nickel, RP, Hor., Lapua and FC) and 6 calibers (223 Rem, 6.5x284, 308 Win. 300 WM, 338 WM,338 Edge) and have come to the same conclusion. That is, if you wish to sort brass for consistency, do it by measuring internal volume.
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