An injector device includes an injector body that receives a syringe; and an injection assembly being configured to dispense medicament from the syringe in a dispensation step. Certain types of injector devices include a sudden completion indicator that indicates when the injection is completed. Certain types of injector devices are configured to dispense two different medicament formulations having different viscosities from syringes without making any changes to the injector devices other than to switch out the syringes. Certain types of injector devices include safety arrangements that inhibit firing of the injector device until front and rear housing assemblies are disposed in predetermined rotational and axial positions relative to each other.