The 450 Magnum Express was developed by North American Arms in 1981 although it was not made available until 1984. It is actually nothing more than the 45 Winchester Magnum that was lengthened to 1,344 inches and the cases were made for them by Winchester. The original loading was the 260gr. Sierra JHP. The cartridge was used in the NAA Eagle single-action revolver. It never gained popularity as a result of crimping problems in fitting a rimless cartridge in a revolver. (Erlmeier, Brandt Ref. 448A)