This being the newbie section, I would suggest against firing while unscrewing your tank.
Its a bad habit to get into, but if you must, MAKE SURE YOUR BARREL SLEEVE IS ON (not a barrel plug).
If your chopping orings while you unscrew, its usually because your unscrewing the tank while its pointed down.
This is usually the wrong way to do it with 'normal' co2 tanks. When you do it, liquid co2 comes out of the tank and freezes the oring, causing it so slice.