A couple of other things to consider:



The very early versions of the Lee rifle had a separate bolt head, but it was NOT threaded to the bolt body. There was a hardened retaining screw that retained the bolt head. thus NO "helical drive" / movement at that end of the bolt..

All of the "threads" in a No1 and No 4 are right-hand; locking recesses / lugs included..

Looking closely at a closing action, the bolt is cammed forward on the 1:1/10 inch locking helix of the bolt locking lugs and body recesses / surfaces. At the same time, the RH bolt head thread is drawing the bolt head rearward; into the bolt body. If the bolt head thred were LEFT hand, it would be driving the bolt head AWAY from the bolt body as it rotated. The old geezers put quite a bit of thought into their product. There is probably some clever little vegemiteicon out there who has built a 3D animation of this behaviour.