Dunno how I missed the 308 part...
Anyway, yes IMHO if the cleaners used had ammonia, it could make the brass brittle. BUT IMHO there are other weaker spots than where that turned loose. IE it should rear its head in the neck/shoulder area first if the complete cases were brittle, not down where it did.
As to not letting go on the first firing, the strength of the area in the web basically were it let go, is so strong I could easily see that the first one weakened etc and the 2nd or 3rd or whatever allowed it to let go. Minor crack first... major one second if that makes sense.
Its exactly how I end up with neck splits... and thats from worn out and brittle brass... they don't split the first time, more like the 15th time...
Now that you say 308... PM me if you want to get rid of it. I never do have enough LC 762 brass around
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