[666]

It is the ejector screw.

Without it the empty cartridge would not eject.

Take it out and try cycling a round.

Screw it in too tight and your bolt will not operate correctly.

Too loose and the brass will not kick out.

Clever those designers, weren't they?

 

[666]

I discoverd that when using no D&T mounts on #4 type rifles, that use the ejector screw for the front mounting with a longer replacement screw, B square etc. If the replacement screw was not screwed in exactly to the right length of protrusion into the receiver. The empty cartridge would not eject. Adjusting the screw fixed the problem.
All rifles had new extractor springs.

It is possible this was a fluke on my rifles, but I would be curious to hear about real world testing done by others at the range.

Remove the ejector screw and see if it alters the ejection.

I can see where an empty cartridge ejects before reaching the ejector screw.

It is possible the extractor springs from Numrich were not new, like the ones from SS.