High Quality Content by WIKIPEDIA articles! The .458 Winchester Magnum is a belted, straight-taper cased, dangerous game rifle cartridge. It was introduced commercially in 1956 by Winchester and first chambered in the Winchester Model 70 African rifle. It was designed to compete against the .450 Nitro Express and the .470 Nitro Express cartridges found in big bore British double rifles. The .458 Winchester Magnum remains to this day one of the most popular dangerous game cartridges. Most major ammunition manufacturers offer a selection of .458 ammunition for rifles chambered in the cartridge.