On the Fox, I have to wonder as did another poster if the frame did not perhaps fail first and the 'double' was, in fact, a very quick second shot that simply further opened the crack. I am also assuming that the gun had double triggers, but don't know that for a fact as it was not stated.
On the Elsie w/the bbl split, I have seen some realy nasty gouges in some bbls that had early steel shot loads fired through them. Some of the early steel shot loads did not have very strong wad petals and the shot would scrub completely through the plastic and gouge the bbl. I'm not saying that is what happened, only that it might be a possible cause. I have also heard of gravel and other things being loaded in lieu of lead shot in times past in the days of card and fiber wads.
I have seen several old Ithacas with lateral scratches in their bbls., but I had/have no way of determining the causal factor[s] that put them there.
I recall a situation where battery elecrolyte could in some situations contact the very hard carbon steel of a motorcycle chain and if it did, the side plate would crack causing a catastrophic chain failure. That failure [crack] could be duplicated on the bench in a static contamination test with zero load involved! Just something to keep in mind about compatibility of certain materials and chemicals.
Lastly, cracks can often be examined by someone trained in such matters to determine the 'nature' of the crack or 'type'. Fatigue cracks are generally dif in appearance from catastrophic failure cracks and or chemical caused cracks, but not always. Just some thots.
Very glad that you were not injured. Your Fox can be replaced.
