A method of connecting a cartridge having a connection feature to an automatic injector having a motor, wherein the cartridge is interconnected to a needle at its distal end and mechanically coupled to a plunger driver at its proximal end.The method comprises lowering the cartridge while being mechanically coupled with the plunger driver into a receiving frame of the automatic injector； sliding the cartridge in a direction of the distal end until reaching a distal stop； linking the connection feature to an interference element of the receiving frame； snapping the connection feature, such that disconnection of the cartridge is inhibited； and containing forces generated by the plunger driver on the cartridge through said receiving frame, thereby immobilizing said cartridge with respect to the automatic injector.
