The .458 Winchester Magnum is a belted, tapered dangerous game hunting rifle cartridge introduced commercially in the mid-1950s.

History[edit | edit source]

First introduced commercially in 1956 and first chambered in the Model 70 Super Grade African safari rifle, the .458 Winchester Magnum was developed to emulate the performance of British double rifle cartridges in a bolt-action rifle. Bolt-action rifles provided a cheaper alternative to the exorbitantly-priced double rifles, and the ammunition could be manufactured via available tooling equipment.

It soon became a success as dangerous game hunters adopted the cartridge, with game wardens, wildlife managers, and professional hunters soon following suit. The .458 Winchester Magnum became the standard African dangerous game cartridge as a result.

However, by 1970, technical problems came to light. Winchester had been using compressed ball powder loads for the cartridge as the propellant. Because of the powder charge clumping and the erratic burn characteristics associated with those kinds of loads, the cartridge's performance came into question.

Though Winchester addressed the issue, the stigma lingered on, and the cartridge's performance on dangerous game was suspect. Nonetheless, the .458 Winchester Magnum remained the standard of measure.

Design Details[edit | edit source]

The large-caliber .458 Winchester Magnum (herein abbreviated as .458 Win Mag) was designed from the outset to duplicate the performance level of the .450 Nitro Express and .470 Nitro Express (herein abbreviated as .450 NE and .470 NE, respectively) cartridges, which had become the mainstay of African game hunters.

The .450 NE was rated to launch a 480 grain (31.1 grams) bullet at a muzzle velocity of 2,150 feet per second (655 meters per second) out of a 28 inch (711 millimetres) barrel, and the .470 NE a 500 grain (32.4 grams) bullet at 2,125 feet per second (648 meters per second) out of a 31 inch (787 millimetres) barrel.

The design criteria for the .458 Win Mag called for it to fire a 510 grain (33 grams) projectile at 2,150 ft/s out of a 26 inch (660 millimetres) barrel. The .458 Win Mag's case is adapted from that of the .375 H&H Magnum, with the case shortened to 2½ inches (63.5 millimetres) and re-necked, not only to reduce taper, but also to accept a .458 inch diameter (11.63 millimetres) bullet. It is the largest of Winchester's standard length magnum cartridges, which includes the somewhat outdated .264 Winchester Magnum and the popular .338 Winchester Magnum.

Though the case volume varies between manufacturers, the typical Winchester case capacity is 95 grains of water (6.17 cm3).

SAAMI recommends a 6-groove barrel with a twist ratio of 1:14 inches, a bore diameter of .450 inches (11.43mm) and a groove diameter of .458 inches (11.63mm), with each groove having an arc of .150 inches (3.81mm).

The maximum pressure recommended by SAAMI is 53,000 c.u.p., while the C.I.P. mandated a pressure rating of 4,300 bar (62,000 psi).

Performance[edit | edit source]

The original design specifications for the .458 Win Mag called for a 510 grain bullet to be fired at a muzzle velocity of 2,150 ft/s. Winchester had both achieved and surpassed these requirements with the cartridge.

Current performance standards for the .458 Win Mag allow it to shoot a 500 grain bullet at 2,150 ft/s through a 24 inch barrel. 500 grains is seen as the standard weight for a .45 caliber bullet. The projectile has a sectional density of .341 inches, providing it with high penetrative figures at a given velocity. The 500 gr .45 bullet has the highest section density among the standard sporting cartridge bullets.

Although bullets such as the 250 gr (16 g) .30 caliber (7.62 mm) bullet with a sectional density of .374 inches, and even a 600 gr (39 g) .45 caliber (11.43 mm) with a sectional density of .409 inches exist, these weights are not seen as a standard for those calibers.

The cartridge, loaded with a 500 gr solid bullet, provides sufficient penetration for dangerous game animals up to and including elephants thanks to the projectile's exceptional sectional density.

Drawbacks[edit | edit source]

The casing length was shortened to work in .30-06-length bolt actions, meaning that there was little room for powder charge.

Because of the case's relatively short length and powder column, longer projectiles and those with a lower weight-to-length ratio may take up valuable powder space, causing lower velocities and reduced performance.

Due to the ball powder charge being compressed, it coagulated in the African heat, causing erratic burn patterns and affecting the cartridge's performance significantly. As a result, velocities were lower than what was advertised. This lead to reports of bullets actually deflecting off of the thick hide of elephants.

Even though the design specifications called for 2,150 ft/s out of a 26 inch barrel, hunters wanting to use a lighter, handier, and faster-swinging rifle gravitated towards sporting weapons with shorter barrels. As expected, shorter barrels lead to reduced performance and lower attained velocities.

Trivia[edit | edit source]

External Links[edit | edit source]

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