Huvius,
It might help fired cases to clear the right action rail during ejection.
I've seen a couple of 98's which had their extractor claw modified for smooth feeding, that had trouble ejecting the last case in the mag, especially if the bolt wasn't worked back fast.
The last fired case would drop down toward the follower as it cleared the chamber during extraction, due to the now empty mag, then as ejection was taking place the case would snag on the right rail, fail to eject and end up sitting back on top of the follower.
This was caused by lack of extractor claw pressure on the case rim as the claw had been modified to aid cartridge feeding.

Just a guess on my part, and the screw's function is likely to be something completely different.

Very nice rifle by the way.