He wants to use the larger nozzle on the HP-B and it won't work because the aircap and how it mates with the body of the HP-B is smaller than the HP-C. All you've done is screw in a smaller nozzle ... and if you're happy with it great ... but it's nothing like a Micron.
40k minis: If all you want is a the small cup style why not just go with the Eclipse HP-BS ... It's a nice airbrush and I use it for touch ups because it's easy to clean ... the head design of the Eclipse is much better suited for paint that the High Performance.
Paul