My working hypothesis, and feel free to post yours:
1. An unknown (and likely never known) something obstructed the bore
2. Pressure rose proximal to that obstruction.
3. The rise in pressure caused a bulge, which caused the rivelling.
4. The rise in pressure caused the expansion of the base of the hull's steel head, and the extractor left an imprint on the head (both described by Burrard)
5. When the capacity of the chamber/barrel proximal to the obstruction to contain the pressure was exceeded, the barrel blew (in at least 2 pieces but NOT along ribband weld lines), possibly starting at the area of embrittlement.
IF METAL FATIGUE IS PRESENT, microphotographs will show evidence thereof. Adam described it as the appearance of the sand at the edge of the shoreline ie. layers of wavy lines.
