In one embodiment there is an injector comprising a housing having a proximal end and a distal end, a shell, a plunger, a needle guard, a first member, and an actuation assembly. The shell may be within the housing and may have a cavity to receive at least a portion of a medicament chamber. The shell may be moveable with respect to the housing from an initial position to an injecting position. The plunger may be moveable with respect to the shell. The needle guard may be moveable between an extended position and a retracted position. The first member may be within the housing. The actuation assembly may be coupled to the housing and the shell. The needle guard may move the first member with respect to the housing as the needle guard moves from the extended position to the retracted position. The actuation assembly may move the shell from the initial position to the injecting position when the first member moves with respect to the housing. The actuation assembly may move the plunger with respect to the shell when the shell is in the injecting position.
