Ammunition having an integrally formed, polymeric casing is provided. Plastic casings for ammunition may be made using injection molding processes for combat ammunition, target ammunition and blanks. The casings, in one embodiment, include a hollow tubular member with an open end and a closed end having an aperture for a primer cap. The base of the casing includes a conical shape within the tube that narrows toward the base. An annular groove and an annular rim are disposed about an outer periphery of the base. Plastic casings may be utilized for ammunition cartridges used in pistols, rifles and shotguns, and are lighter and less expensive to manufacture than traditional brass casings. Further, the polymeric casings may include any desired colorants to distinguish different calibers of ammunition by color, and the spent casings may be recyclable.