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The take down feature means the chamber is split. There is a joint in there that should match up quite tightly. I have seen a 97 where the barrel is fit poorly, or gets out of alignment or something and there ends up being too much gap in the joint in the chamber. Then brass can swell into the gap and lock it up tighter than a frog's arse.
I have an old model 12 when they made the Trench guns, they don't often fail, mine has not either in all it's years. Perhaps you should go to a gunsmith, I think your extractor mech. has retired.