Jinhao cartridges

I just received my first fountain pen, a Jinhao X450, and a box of Jinhao ink cartridges. When I inserted one as the illustration on the box showed and reassembled the pen, I expected the end of the cartridge to be penetrated and ink to flow into the nib. Not only did it not break, I was later unable to force it (using far more force than is reasonable). What am I doing wrong?