Thanks Steve - it's interesting that the Winchester and PMC cases were heavier than most of the rest, but had the largest measured case capacity...
"measured case capacity" can be wildly innacurate, unless you're doing something to ensure the outside dimensions of each case are identical. It's important to think about the difference between a case sitting there on your bench, and the same case under pressure formed to the chamber walls when it fires. What you're measuring on the bench is not the same, and there can be significant capacity differences between otherwise identical cases.
Even if the cases were all fired in the same rifle (or sized in the same FL die), variations in brass hardness means variations in spring-back from the chamber or sizing die walls, which results in case capacity differences. In my experience, case weight is a much more accurate indicator of actual capacity.
There can be some error in sorting by case weight, but the biggest uncontrolled variable there is the dimensions of the extractor groove. Every other area of the case is enclosed by the chamber and bolt, and additional brass in any of those areas directly correlates to case capacity during the firing cycle.
