The present invention relates to medicament injection devices (100). A cartridge (600) with a septum and a needle unit (500) having front and rear needles (510, 520) are configured for relative movement from a state where the septum is sealed to a state where the septum is pierced by the rear needle (520). The injection device (100) may include a needle shield (350) and be configured for piercing the septum by the rear needle (520) when the front needle (510) is operated relative to the needle shield (350). The injection device (100) may also include a damping mechanism configured for limiting the speed of movement of the cartridge relative to the needle unit. The injection device (100) may also include an indicator generating a signal when a piston driver has travelled the complete stroke length, wherein the indicator has a deflection element that is deflected prior to or during movement of the cartridge relative to the housing.