Like what Dust said, you need to be mindful of the materials you are making this out of. Schedule 40 PVC piping has a working pressure right around 250 or so PSI I believe, which is way below what Co2 pressure can peak at. I have a launcher that was made years ago that uses a metal paintball expansion chamber to store the gas from a 12 gram Co2 cartridge. Browse some paintball info sites, and I am sure you will find a host of ideas that you can use.
