The internal capacity at peak pressure is all that matters and the weight of each individual piece of brass has everything to do with internal capacity--sorry but that is a fact.
The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.
Well, your both barking in the right direction..
In reality the chamber volume, case volume, and where the bullet is all change as pressure builds up during the ignition/burn sequence. Then you throw in chamber temperature and burn retardants (lube, etc) into the mix.
The chamber expands, that's what strain gauges detect when they measure chamber pressure. The case of course expands with it. Even the bolt can deform and snap back. The bullet starts to move down the barrel at a relatively low pressure. Max pressure does not occur until the bullet is a couple of inches down the barrel.
So this dynamic set of events are hard to predict. To model it, one has to go to an engineering firm that specializes in fluid flow computational analysis, and further, the modeling software they use MUST be able to handle a moving object in the stream, as well as changing volume - there are only a couple of very expensive packages that can do this kind of modeling.
Well, outside of that we experiment and try different case prep processes to try and find the factor(s) that makes the most difference. It's not exact, and that leads to comments like the above. The bottom line, think through and consider ALL factors that influence the burn sequence, consider that steel DOES deform and move about, then spring back. Then prioritize and select those factors that you think will make the most difference to your shot-to-shot consistency.
Kyle Precision Arms