An injector includes an injector housing, an activation button assembly translatable from an unactuated position to an actuated position and a cartridge door movably mounted to the injector housing between an open position and a closed position. A deflectable interference member has a resting position configured to limit an insertion depth of a cartridge into an interior channel of the cartridge door to a sealed position, wherein the cartridge piercing needle does not fully penetrate a pierceable septum of the cartridge. Movement of the activation button assembly from the unactuated position to the actuated position thereof, in the closed position of the cartridge door, deflects the interference element out of the resting position thereof, thereby enabling further advancement of the cartridge into the interior channel of the cartridge door to an unsealed position, wherein the cartridge piercing needle fully penetrates the pierceable septum.