Homemade air rifle

[Cactus]

Hi there everyone, im completely new to this forum and am looking to build my own air rifle/gun and need some info on the best means and methods to do so...
First, a list of 'minimum' requirements...
The rifle must:
-Be self sufficient (no external source of air)
-More than one shot in the same fill
-look good
-breech, not muzzle loaded

I so far have rounded up an old fire extinguisher (approx 1.5L) a 12v battery, a 1m 1/2'' legnth of copper pipe a switch to control a solenoid a two direction contol valve (http://g01.a.alicdn.com/kf/HTB11FzYJFXX ... nual-b.jpg) and a regulator.
Im hoping to build the extinguisher into the stock aswell as the battery if needed.
I have some experience in the 'shop and have a fairly large range of bith woodwork and metalwork tools, i am mostly wondering what the best(and most compact) valve to use would be...
Any help would be appreciated!! Thanks :bounce:

[farcticox1]

I normally start with a layout plan, then change things around and build something completely different