Magnetic helices and skyrmions in noncentrosymmetric magnets are representative examples of chiral spin textures in solids. Their spin swirling direction, often termed as the magnetic helicity and defined as either left handed or right handed, is uniquely determined by the Dzyaloshinskii-Moriya interaction (DMI) in fixed chirality host crystals. Thus far, there have been relatively few investigations of the DMI in metallic magnets as compared with insulating counterparts. Here, we focus on the metallic magnets Co8-xFexZn8Mn4 (0 <= x <= 4.5) with a beta-Mn-type chiral structure and find that, as x varies under a fixed crystal chirality, a reversal of magnetic helicity occurs at x(c) similar to 2.7. This experimental result is supported by a theory based on first-principles electronic structure calculations, demonstrating the DMI to depend critically on the electron band filling. Thus by composition tuning our work shows the sign change of the DMI with respect to a fixed crystal chirality to be a universal feature of metallic chiral magnets.