pneumatic axe

hi everyone

i am quite interested in building a pneumatic axe like little hitter, but i have no idea how i would get the compressed gas to make the axe move. Would you use a ram, or would you have to get something else? because i can't find any powerful but featherweight sized rams anywhere.
Also, i have a 400 psi compressor, is this likely to be enough?
One final question, where could i get a suitable gas tank?

Everything you need to know is on here;

http://www.teamonslaught.fsnet.co.uk/inde.htm

co2 is supplied at events by the EO.

ahh, i understand now, thanks
another noob question :(
how should the ram be attatched to the axe?

http://www.teamdavinci.com/understanding_pneumatics.htm

thanks a lot for the help guys.
I will probably start building this in the next few weeks.