I was shooting CFA's 500/465 H&H when it blew up. I have done a lot of research in this in this area. I know of several other doubles that have "blown" up bbls. My theory is this.
There are some double rifles out there that have defective steel. No matter what powder you use the bbl will burst.
This has occured in several H&H Dominions.

Double rifles after 1910 to 1915 seem not to have this problem.