This is a hot end style i am using for my bowden designed printer, but it should work for any hot end. it allows easy flow of material through a simple staged melting process that allows heat to effectively propagate though the feedstock changing viscosity of liquid and reducing internal pressure. not much else is understood other than it takes less force to extrude 3mm feedstock.
here is a picture
here is the code to generate the image above it was created in openscad linked in thingiverse
also referenced here http://www.thingiverse.com/thing:31851