Anyone else here feel free to chime-in, but it sounds to me like you need to anneal your cases.
This is REALLY common on a whole pile of new 223 WSSM brass. The brass is VERY hard from the factory. Once fired, the case stretches some and gets even harder. Full length sizing moves the brass, but it "springs" back to fired dimentions. Typically you can feel the resistance when closing the bolt on that brass as well.
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