A method of closing the distal end of an ampoule (322) is shown. The ampoule (322) has a variable diameter head portion (331) having a locating surface (350) and an opening. A septum (327) is positioned on the opening and secured to the head portion (331) with a ferrule (324) using a plunger. The plunger exerts a force in a proximal direction to press the ferrule (324) on the head portion (331) until the press causes the ferrule (324) to contact the locating surface (350). Further, the ampoule (322) for use in a cartridge (320) for a drug delivery device (100) 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 (100).
