The whole thing may never be truly understood - unless and until we find a way to observe what actually happens inside a cartridge. Right now, we cannot. What we "observe" now are merely secondary or even tertiary results of what happened. We guess at pressures based on what effect that pressure has on something else, for example. We observe long-after-the-fact effects and infer a cause, but we cannot directly observe the process at all, much less in anything like real time.
