.458 Winchester Magnum

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.458 Winchester Magnum

Type	Rifle / Hunting
Place of origin	USA
Production history
Designer	Winchester
Designed	1956
Specifications
Parent case	.375 H&H Magnum
Case type	Belted, tapered
Bullet diameter	.459 in (11.7 mm)
Neck diameter	.481 in (12.2 mm)
Base diameter	.513 in (13.0 mm)
Rim diameter	.532 in (13.5 mm)
Rim thickness	.220 in (5.6 mm)
Case length	2.500 in (63.5 mm)
Overall length	3.340 in (84.8 mm)
Rifling twist	1-14"
Primer type	Large rifle magnum
Ballistic performance
Bullet weight/type	Velocity	Energy
300 gr (19 g) HP	2,606 ft/s (794 m/s)	4,525 ft·lbf (6,135 J)
350 gr (23 g) RN	2,557 ft/s (779 m/s)	5,083 ft·lbf (6,892 J)
400 gr (26 g) FN	2,468 ft/s (752 m/s)	5,411 ft·lbf (7,336 J)
500 gr (32 g) RN	2,192 ft/s (668 m/s)	5,336 ft·lbf (7,235 J)
Test barrel length: 26" Source: Accurate Powder ^[1]

The .458 Winchester Magnum is a rifle cartridge introduced 1956 by Winchester. The cartridge case is based on the .375 H&H case shortened to 2.5 in (64 mm), and "blown out" (case opening enlarged) to accept a bullet of .458 inch (11.6 mm) diameter. With good handloads one can expect approximately 2,170 feet (660 m) per second (660 m/s) using 500 grain (32.4 g) bullets (achieved using a barrel 24 inches (610 mm) in length). It can be loaded with bullets as light as 300 grains (19 g).

Winchester no longer sells ammunition in .458 Winchester Magnum, but other manufacturers do. Hornady offers what they call a "heavy magnum" loading that features a 500 grain (32.4 g) bullet with a velocity of approx 2,260 feet (690 m) per second (690 m/s). They use a special double-based cooler burning propellant ("powder") not available to the public for handloading. This innovative loading allows the .458 Winchester Magnum to attain 5670 foot pounds of muzzle energy. Federal Cartridge is now loading a 500-grain (32 g) Barnes X bullet with a sectional density and ballistic coefficient that allows it to maintain approximately 2000 foot pounds of energy at 500 yards (460 m) and a flatter trajectory that has never been attained with this cartridge and bullet weight. Numerous companies offer rifles in this caliber, including the Winchester Model 70.

The rounds for the .458 Win mag are expensive, making handloading a worthwhile effort. The recoil of the factory loads is about 70 foot pounds. Handloads can be made that will make this cartridge more comfortable to shoot, for example using a 300-grain (19 g) Cast lead bullet at 1,282 ft/s (391 m/s). ^[2]^[1]