An auto injector for administering injection of a medicament from a cartridge containing the medicament, the auto injector comprising: a housing; a cartridge receiver with a cartridge receiver compartment configured to receive a cartridge and/or a cartridge assembly, with at least one cartridge retention member, when inserted through a cartridge receiver opening along a longitudinal axis in a receiving direction; wherein the cartridge receiver has a passage through which the at least one cartridge retention member travels at least in the receiving direction, and a member preventing movement beyond a retention position in a direction opposite of the receiving direction; an elongated ejector that is configured with: an ejector support face for supporting the cartridge or cartridge assembly, a longitudinal ejector slot extending towards the ejector support face from an ejector rest portion; wherein the elongated ejector is suspended to move along the longitudinal direction and is spring-loaded in the direction opposite of the receiving direction; and an ejector lock supported for turning at least a fraction of a revolution and maintained in a longitudinal position relative to the housing; wherein the ejector lock has an ejector lock support portion that is configured to align with and slide along the longitudinal ejector slot at a first angle and to be brought to align with the ejector rest portion at a second angle wherein at the first angle, movement of the cartridge assembly is allowed and at the second angle, movement of the cartridge assembly is restricted in the receiving direction at least from moving beyond a predefined longitudinal position. a housing; a cartridge receiver with a cartridge receiver compartment configured to receive a cartridge and/or a cartridge assembly, with at least one cartridge retention member, when inserted through a cartridge receiver opening along a longitudinal axis in a receiving direction; wherein the cartridge receiver has a passage through which the at least one cartridge retention member travels at least in the receiving direction, and a member preventing movement beyond a retention position in a direction opposite of the receiving direction; an elongated ejector that is configured with: an ejector support face for supporting the cartridge or cartridge assembly, a longitudinal ejector slot extending towards the ejector support face from an ejector rest portion; wherein the elongated ejector is suspended to move along the longitudinal direction and is spring-loaded in the direction opposite of the receiving direction; and an ejector lock supported for turning at least a fraction of a revolution and maintained in a longitudinal position relative to the housing; wherein the ejector lock has an ejector lock support portion that is configured to align with and slide along the longitudinal ejector slot at a first angle and to be brought to align with the ejector rest portion at a second angle wherein at the first angle, movement of the cartridge assembly is allowed and at the second angle, movement of the cartridge assembly is restricted in the receiving direction at least from moving beyond a predefined longitudinal position.