A method of closing the distal end of an ampoule is shown. The ampoule has a variable diameter head portion having a locating surface and an opening. A septum is positioned on the opening and secured to the head portion with a ferrule using a plunger. The plunger exerts a force in a proximal direction to press the ferrule on the head portion until the press causes the ferrule to contact the locating surface. Further, the ampoule for use in a cartridge for a drug delivery device has non-standard dimensions to provide a coding system to reduce the risk of a user dispensing the wrong medicament from the drug delivery device.
