Crossman 600 Question

Does anyone have a Crosman 600? I’ve never owned one before and I received one today that has had some modification done to it that eliminates the piercing cap. Apparently you are just susposed to screw the end cap down to pierce the co2 cartridge. Every time I do this, the Co2 just blows out everywhere. Is there some trick to installing the cartridge? I’d hate to think I got a F’d up gun out of the gate, but I’m at a loss here.