I appreciate that you're looking where the facts seem to take you. On the surface of it, there would not seem to be a requirement for a very large pressure spike to cause this particular failure.

Maybe the lab folks would confirm your calculation and comment on possible adjustments to the formula because of the rapid rate of the pressure change. Maybe they'd comment on how the tensile test sample failures compared to barrel blowout.

You've mentioned recommending loads as intended for the original gun. Probably a good guideline and possibly easy to run questionable pressures without obstructions. Really looking forward to the article, nice job.