Apparatus and methods for delivering medicament to a patient. The apparatus may include elements with different capacities to attenuate or absorb sterilizing radiation. The apparatus may include a medicament delivery assembly with interactive elements for dose-setting, priming and medicament ejection. The assembly may include a chamber housing a radiation-sensitive medicament present in the apparatus during sterilization by electron beam. The assembly may include an actuator chassis, a drive mechanism, a needle-priming mechanism and a fluid-displacement mechanism including a fluid-displacement member. The chassis may be fixed, relative to an outlet, to the chamber. The member may be slidingly and/or threadingly engaged with the chassis, and may be configured to move relative to the outlet to deliver the medicament through the outlet. Assembly elements may be nested coaxially and/or stacked axially. The assembly may include at least one hollow region. The hollow region may reduce beam attenuation or reduce radiation absorption.