A system for sequentially dispensing a non user settable dose of one medicament followed by a user settable dose of a primary medicament. The system may include a dual cross section floating piston (210 310) arranged to facilitate first delivering all or substantially all of a given medicament (e.g. a secondary medicament) through an output needle (208 308) and then thereafter delivering yet another medicament (e.g. a primary medicament) through the same output needle in a single injection step. The dual cross section floating piston of the system also reduces or limits ullage left in the medicated module relative to the amount of the secondary medicament dispensed from the system.
