Take a threaded PVC connector and two end caps, cut a short section of PVC (it should be wide enough to fit a 12 gram co2 cartridge inside, the cartridge should slide up and down easily) drill and de-burr a lot of holes in the short PVC section. Using PVC cement attach the short PVC section to one of the caps, then screw a sharp screw through cap so it pops out in the middle of the short PVC section. Remove the screw and grind/ file the end to a sharp point (this is to prevent the co2 cartridge from snagging on the screw) put the screw back in the cap. In the other cap drill a hole that will fit a small bolt, the head of the blot should not be able to pass through the hole, drill four small holes in the cap, place the bolt in and attach a nut to the bottom of the bolt a few turns down from the end. Using PVC cement attach the short pipe/cap screw assembly to one end of the connector. Place a 12 gram co2 cartridge with the seal end facing the screw in the short pipe. Fill with paint. Teflon the threads to your bolt cap and screw it on (the bolt should rest on the cartridge) there you go! One mine.