He may have degassed it, but not fired off what was in the valve chamber.Was the gun gassed up when you tryed to remove the cap???????
Only reason i ask is that unless the gun is gassed up the cap should come out easily. Have seen them where some idiot has swung on it with what seems like a airgunThese really do not need to be that tight if they are done up to the correct torque then they should come out easily and there is no need for a karma stainless one.