Thank you Thunderbox. I couldn't remember specifics about the cases I'd heard about but your post has jogged my memory. Yes, they had aftermarket springs fitted! The springs were not finished smoothly on the ends, leaving a sharp step which created the grip.
Just to add to what Peter is saying, here's a pic showing the cam lug on top of the cocking piece. If this is missing, opening the bolt will not be engaging the cam lug which would make bolt lift very easy. It will also be causing a dangerous situation where the striker can be present through the bolt face while cycling the action until the cocking piece engages the sear. This is because the lug would normally be holding the cocking piece and striker back a little in the short cam groove once the handle is lifted.
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