Shotgun or Rifle Mics ? Design ?

[MottledGreen]

Hi, I am looking for info for designing a shotgun or rifle mic assembly for a school
project.
Specifically, long distance outdoors with human voice / speech frequencies.

Mic output would go to an existing pre amp.
Any info on construction materials, dimensions, mic insert types would be
much appreciated. I realise that some dimensions would be based on the wavelength of the desired frequency range (50Hz-6Khz), which are easy to work out using the speed of sound formula, but which dimensions ?
I have a design for a rifle mic constructed in an organ pipe style, but are unsure of the construction material to use for this or the shotgun mic. Metal or PVC pipe ?

The mic I was intending to use would be a condenser type but any advice on which and how to mount it would be appreciated.
No FAQ or Web info available; I just spend 12 hours looking !

BTW I cross posted this on the "Microphones" board.