An auto injector (4) for administering injection of a medicament from a cartridge containing the medicament, the auto injector (4) comprising: a housing (6)； a cartridge receiver (300) with a cartridge receiver compartment (302) configured to receive a cartridge assembly (600), with at least one cartridge retention member (808), when inserted through a cartridge receiver opening (301) along a longitudinal axis (L) in a receiving direction；wherein the cartridge receiver (300) has a passage (316) through which the at least one cartridge retention member (808) travels at least in the receiving direction, and a member (312) preventing movement beyond a retention position in a direction opposite of the receiving direction； an elongated ejector (200) that is configured with: an ejector support face (204) for supporting the cartridge or cartridge assembly (600), a longitudinal ejector slot (228) extending towards the ejector support face (204) from an ejector rest portion (206)； wherein the elongated ejector (200) is suspended to move along the longitudinal direction and is spring-loaded in the direction opposite of the receiving direction； and an ejector lock (212) supported for turning at least a fraction of a revolution and maintained in a longitudinal position relative to the housing (6)； wherein the ejector lock (212) has a ejector lock support portion (214) that is configured to align with and slide along the longitudinal ejector slot (228) at a first angle and to be brought to align with the ejector rest portion (206) at a second angle.
