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sharp pointy paper clip with a right angled bend in end about 3mm long...scratch the inside of case as hard as you can....if there is a fault it will "catch" try it on the ones that are buggered and...

only bump it as much as you need to be able to chamber freely..... and PLEASE paperclip test ALL your brass before loading it up from here on in.....
its a real pain in arse if you get a seperation...