Abstract: In one aspect, a medical injector is provided herein having a body and an overcap releasably attached to the body configured to prevent mounting of a needle prior to mixing of components within the body. In a further aspect, a slidable collet may be provided useable to urge resilient members from an outward disrupted state inwardly to collectively define a needle mount. Advantageously, a medical injector is provided which ensures proper sequence in preparation of the device, particularly with respect to the step of allowing mounting of a medical needle to the device subsequent to preparation of the medicament to be administered.