I have a Blackburn Airshot that has worked nicely since March of this year. Yesterday I went to use it and it was out of air. I ran through 3 cartridges trying to install a new one. They all immediately leaked air once I began screwing them into the Airshot. I've only replaced a cartridge once, not long after I got the Airshot but that worked fine. Not sure what is going on now. Any one have some ideas? Is this thing defective all the sudden?