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If there is no debris in the bolt, it may be the spring. Curiously a weak mainspring can lead to blown primers which leave metal bits in the bolt which can interfere with the function. This happened to me with a ruger m77. A new main spring solved the problem . There was no way to diagnose the problem based on cartridge analysis since the primers looked ok.
All that said, giving the firearm to a good Smith is the best option.
