A method of using a syringe and a flexible member is described. In some versions, the method may involve providing a syringe, a needle, a pre-filled cartridge, an adapter, a flexible member, a biasing element, and a guard. The method may involve retaining the guard, releasing the guard by actuating the flexible member to translate the guard in the distal direction to cover the needle, and locking the guard. In some versions, the flexible member may have a first and second position for actuation. In some versions, the flexible member may engage and disengage the guard to retain and release the guard.
