dearmer,
Just for information, slow powders in rifles can cause blowups. A famous example is the case of 270 Win. loaded with less than the recommended amount of 4831. This is another one I have never seen but has been reported enough that it must have happened. Enough cautions have been given about this that instructions for loading 5.6X61 vom Hofe S.e. make particular mention of it. Also One of the Engineer BNs I was in ran a quarry for training. Military Dynamite was used in blasting( fairly slow) with good success, but when the ran out and used some C4 (much faster)they didn't get dust, the got chunks as large as house trailers, whish had to be blasted again to get them small enough to fit into the crusher. The Dynamite would "heave" it, but the C4 would "shatter" it along fault lines. I don't know if this affects your examples or not.
Mike
