If you look at the decades-old data from Dr. Brownell, the evidence for instability in light loads of slow burning powder is clearly present.
He shows a graph of pressure vs. load. In the lower part of the curve, greatly increased pressure variability is clearly present. Undoubtedly, he noticed that effect. But, as far as I have found, he did not comment on it, or what may have caused it.
I have a hard time accepting the notion of pressure waves standing in the cavity, and hold that explanation as tentative. There is just too much you have to assume in order to accept that idea, as far as I can tell. However, SOMETHING clearly happens. Danged if I know what. So I can't criticize that theory, because I don't have anything that is as good, let alone better.
