How do forward-ejecting bullpups work?

[Skribs]

Firearms like the FS2000 and recent MDR have forward ejection tubes so the spent cases don't smack you in the face. How do they reliably get the cases into that tube and push them forward?

 

[Sam Cade]

Like this.
http://www.youtube.com/watch?v=hL1Hz5gBeto

 

[TIMC]

Here is another video that shows the Kel-Tec RFB. I have never had any issues with mine, the ejection port is above the chamber, it seems to work very well,
http://www.youtube.com/watch?v=xM8H49cuFPY