Design & Specifications
The .458 Winchester Magnum was designed from the outset to duplicate the performance level of the .450 Nitro Express and the .470 Nitro Express, which had become the mainstay of African dangerous game hunters. The .450 Nitro Express had been rated to launch a 480 gr (31 g) bullet at 2,150 ft/s (660 m/s) out of a 28 in (710 mm) barrel while the .470 Nitro Express would launch a 500 gr (32 g) bullet at 2,125 ft/s (648 m/s) out of a 31 in (790 mm) barrel. The design criteria for the .458 Winchester Magnum called for it to launch a 510 gr (33 g) bullet at 2,150 ft/s (660 m/s) out of a 26 in (660 mm) barrel.
- SAAMI compliant .458 Winchester Magnum cartridge schematic: All dimensions in inches .
The .458 Winchester Magnum's case was based on a .375 H&H case shortened to 2.5 in (64 mm) and renecked (to reduce taper) to accept a .458 caliber (11.43 mm) bullet. The cartridge remains the largest of the standard length magnum cartridge family released by Winchester, which includes the .264 Winchester Magnum and the .338 Winchester Magnum.
SAAMI recommends a 6 groove with a twist ratio of 1:14 with a bore Ø of .450 in (11.4 mm) and a groove Ø of .458 in (11.6 mm) with each groove having an arc length of .150 in (3.8 mm). While case volume varies between manufacturers, the typical Winchester case capacity is 95 grain of H2O (6.17 cm3). Maximum recommended pressure given by SAAMI is 53,000 c.u.p. while the CIP mandates a maximum pressure of 4,300 bar (62,000 psi).
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