IMHO -Too many variables are being brought into the problem.

If I fully understand, after re-reading the original post, Fred's rifle 'fired' when he closed the bolt on a loaded chamber.

Unless the trigger was accidentally pulled, this would indicate the sear 'nose' (A) failed to adequately engage the 'sear notch' (G) of the Cocking-Piece.

Likely reasons: inadequate sear-spring or stock interference.

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