a pyrotechnically powered needleless injector for introducing predetermined quantities of medicaments interstitially through the skin . the injector includes a barrel formed to receive an ampul . an elongated disposable ampul , containing a quantity of a selected medicament and having an orifice at one end , a deflagatory gas - generating pyrotechnic charge at its other end , and a gas operated piston positioned between the charge and the medicament to eject the medicament through the orifice under high pressure upon detonation of the charge , is adapted to be inserted into and releasably secured in the barrel . the barrel is rotatably and slidably mounted to a housing containing a firing mechanism which is armed by relative motion of the barrel and housing . a triggering mechanism in the housing activates the firing mechanism to detonate the charge within the ampul .