A method includes moving an actuation lock of a medical injector from a first position to a second position. The actuation lock has an extended portion disposed between a shoulder of a housing and the base when the actuation lock is in the first position. The extended portion is spaced apart from the base when the actuation lock is in the second position. A distal end portion of a base, which is movably coupled to an end portion of the housing, is placed into contact with a body. The base is actuated after the placing to release an energy from an energy storage member within the housing to produce a force to move a needle from a first needle position to a second needle position. At least a portion of the needle extends through the base when the needle is in the second needle position.