Dry firing is an okay way to discharge the co2 cartridge, you can also unscrew it and leave it threaded and wait a few seconds for the rest of the CO2 to discharge from the cartridge... But as a general rule I've found (depending on how the gun is tuned) you SHOULD get 20-30 shots out of each 12 gram cartridge before it's empty...
Possibly, but unlikely... Usually after firing the gun 5-10 times or more, there usually isn't enough CO2 to last more than a 1/2 to MAYBE 1 second burst of CO2 coming out.. And even if there is a bit more than that, it usually isn't enough in a 12 gram cartridge to do damage to the cartridge piercing pin..
The seal around the piercing pin is a bit different, and a lot more durable than the usual O rings that go on the larger tanks..
