Re: Weighing brass into groups worth it?
Testing case capacity is like asking what is the capacity of a balloon. The case is simply an elastic liner for the steel chamber.
It expands to conform to the chamber long before the chamber itself begins to expand, and that expansion continues and remains for as long as the bullet it in the bore and pressure is being sustained by that bullet. That expansion is not a constant and corresponds to the pressure curve, which itself varies from shot to shot. Any measurement we make is at best an approximation based on the springback dimensions that only exist prior to actual ignition.
Measurements should be made on fired cases that have had no additional work performed on them.
I believe that there is really only one reliable medium for case capacity measurement, and that medium is the propellant powder I will be using for that load. I use a drop tube to overcharge the case, disregard what falls away, and weigh the remaining charge. That weight gets written on the side of the case with a Sharpie.
After determining capacities, cases are arrayed according to capacity, and the required number are selected from at and around the most dense grouping of similar capacities. They are placed into the loading block, loaded, and fired in relation to that specific order.
My matches consist of two stages, with sighters and scoring shots for each stage. The sighter rounds are selected from the rounds occupying the center of the block, as they will have greatest commonality with those cases whose capacities bracket the center. I start firing cartridges from the center and work toward the end.
This establishes my 100% load density value; and all actual charges are compared against that value, with the caveat that they are only as consistent as the individual capacities are consistent.
There is a lot of thinking about cartridge fabrication that is based on assumptions. One of them is that things happen a certain way, and always do so. We believe that we know the sequences and timings of events, and that they follow a rigid plan. We believe that what we do has direct correlation to this rigid plan.
Would that this were the case, but the very randomness of POI's, however tight, decries these assumptions as at least partly false.
Does case capacity variance make a difference? Of course it does; all handloading variables have significant consequences. But do those differences, once eliminated, also eliminate randomness in the performance of a given set of cartridges? Yes, but only to some degree, not all.
We are all partial slaves to random consequence.
That's why I save the real serious precision for experimental purposes, to better understand real consequences, as opposed to supposed consequences persuant to common knowledge.
I may not be able to explain how and why the presence or absence of a specific technique coresponds to a demonstrable degree of accuracy; but I can demonstrate that it does exist.
I can also choose to apply or refrain from applying that technique in the knowledge that there are compensations that come in the form of more ammo made quicker and easier, and fired with serious application of marksmanship concentration that improves my marksmanship to a degree that represents a fair tradeoff.
It's a matter of recogmizing consequences and their comparative values, and making a choice, or choices.
I don't know if my choices are good ones or the right ones, but I do know they are mine and are based on information I developed at my own hands. I believe that weighing cases may cultivate confidence, but that such confidence may be false. I believe that measuring case volume is more representative, but that it also is not any kind of an absolute indicator of consequential performance.
We do what we can, and some of it helps. Sometimes we don't bother, and what we lose is acceptable in light of other influences. A compromise, like culling extremes, then randomizing what remains, can render a fairly acceptable consequence.
Greg
