I will say the only guns I can recall hearing of "Blowing Open" on firing were those fitted with rotaru bolts. It seems as if that rotary bolt is not very precisely fitted it will with just a bit of thrust cam itself open.
Not exactly sure, but I think you meant that to be within the context of S x S guns, maybe even Ithacas only? Anyway, I have seen other designs come unbolted at the firing of the first barrel, but they were all O/U guns. Perhaps the superposed design lends itself to that greater tendency, particularly if the top barrel is fired first.
SRH
