I bought one a couple of months ago and hadn't used it yet when I met my brother for our usual Thursday ride. Discovered he had a flat before we left. He quikly repaired it with a new tube and floor pump, but didn't have his mini pump. "Don't worry I have this brand new handy dandy CO2 inflator" i say. Sure enough 20km out he gets another flat, and also sure enough the infator didn't work. Tried 3 cartridges--nothing. So i rode back to his place, got the car and rescued him. Took the inflator back to the LBS the next day, and the guy says Yah sometimes they don't puncture the cartridge. He dropped a penny in the bottom of the tube and replaced the cartridge-- worked fine. I'm carrying a mini pump again.