A medicament delivery device (10) comprising a syringe (12) having a barrel with an open end, and an axially moveable stopper (18) received in the barrel separating a first chamber axially forwards of the stopper from a second chamber axially rearwards of the stopper. The medicament delivery device further including an expandable drive housing (24) arranged to receive a propellant from a propellant source (36) for providing a vapour pressure, the expandable drive housing having a narrow channel in fluid communication with the second chamber. The expandable drive housing is expandable upon receiving propellant from the propellant source and, upon expansion, causes forward axial movement of the syringe. Propellant introduced into the expandable housing may pass through the narrow channel into the second chamber and cause forward axial movement of the stopper in the barrel to expel medicament contained in the first chamber through the open end, where axial movement of the stopper in the barrel commences after axial movement of the syringe.