A detachable box magazine for firearms includes a hollow magazine tube extending longitudinally along a median plane. The magazine tube defines a single-stack portion extending to an upper tube end with an upper tube opening. The magazine tube defines a double-stack portion positioned below the single-stack portion and extending to a bottom tube end with a bottom tube opening. For example, front portions of the opposite tube sidewalls have a stepped shape between the upper tube end and the double-stack portion, and the rear portions of the sidewalls have a linear taper between the upper tube end and the double-stack portion.