I apologize in advance if I butcher the nomenclature...

I have been having trouble getting the action to completely close up on my No4 mk1*. What I observe is that the bolt head, riding along the groove in the action of the receiver, turns slightly to the left when it gets to the section of the receiver "rail" near the front of the receiver where you can take the bolt head out of the action groove. This is also the point where cock-on-close process begins compressing the firing pin spring in the bolt.

So as you are pushing the bolt forward, when the bolt head gets to the place where there is a gap in the rail/groove, the bolt head turns slightly to the left and gets out of alignment with the action groove in the receiver. Then the forward travel gets hung up right where the bolt head should re-enter the action groove. You can see the groove in the bolt head is hitting against the groove rail of the receiver because they are slightly out of alignment.

This seems to happen 90% of the time when you are cycling the action with no cartridges in the rifle. If there are cartridges in the rifle, it only fails to close about 25% of the time. If I work the action, keeping the pressure on the bolt head with my finger to keep the bolt head turned fully to the right and in alignment with the action groove, it closes every time.

Any advise on this? What would cause the bolt head to turn? Could it be the firing pin spring causing the bolt head to turn, it seems like it is possible.

Thanks in advance

PS I have made sure that there aren't any burrs on the bolt head or the receiver groove rail causing this.
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