Introduced in 1956, Winchester’s goal with the 458 Win Mag was to offer a rifle and cartridge combination that would match the performance of the vaunted Nitro-Express chamberings from H&H and other manufacturers of double rifles in an affordable standard-length bolt-action rifle. The original loads were rated as generating 5000 foot-pounds of energy by launching a 500-grain bullet at 2120 fps or a 510-grain bullet at 2110 fps. These advertised numbers were chosen so the 458 Win Mag could compare favorably to the advertised ballistics of the double-rifle cartridges it was to compete against. Winchester made two mistakes when conceiving and standardizing this chambering. First, it assumed the advertised ballistics of the Nitro-Express rounds were realistic, which is odd because Winchester had long been advertising ballistics for various chamberings that factory ammunition never achieved. Second, it loaded the original ammunition with a propellant similar to W748 that is notorious for being phenomenally sensitive to temperature. Had Winchester tested the various Nitro Express cartridges it was intending the 458 to compete against, it would have discovered that despite having advertised muzzle velocities typically between 2100 and 2200 fps, none of those ever achieved significantly more than 1900 fps and most were closer to 1800 fps. So, other than marketing, there was no magic to the claimed velocity. The magic was all in bullets built tough enough to hold together and penetrate sufficiently. In loading the 458 to achieve the velocity it believed was needed, Winchester found it had to use an inconvenient 26-inch barrel and load to a pressure level that, combined with the temperature issues of the propellant used, which resulted in pressure spikes, and jammed guns. Soon enough, the word came back: the 458 Win Mag was not impressing folks with its performance in Africa. The chambering never fully recovered from that initial bad press. Winchester reduced load pressure, shortened the barrel, and just continued to claim 2120 fps while actual velocity was closer to 2000 fps but the new combination worked. Folks appreciated the handier rifle and the ammunition did the job and the cases freely ejected. Winchester discovered what the folks making the Nitro-Express ammunition had long-since learned: bullet performance is what matters most when hunting big, dangerous critters with tough hide. Loaded with Woodleigh bullets and modern temperature-stable propellant, the 458 is a perfectly useful cartridge for use against the biggest and meanest of critters anywhere on Earth. Keeping velocity at 2000 fps, or a bit less, has significant value in that it can allow the shooter to recover from recoil and make a follow-up shot faster, should that be required. In this regard, the 458 Win Mag did exactly what Winchester hoped it would do: it offered an effective chambering for African hunting in an affordable gun.