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 2170 feet 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 350 grain (22.7 g). It has been suggested that Break action be merged into this article or section. ... This article does not cite its references or sources. ... Year 1956 (MCMLVI) was a leap year starting on Sunday of the Gregorian calendar. ... The Winchester Repeating Arms Company was a prominent American maker of repeating weapons during the late 19th Century and the early 20th Century. ... .375 H&H Magnum The . ... .357 Magnum cartridges, containing bullets A bullet is a solid projectile propelled by a firearm and is normally made from metal (usually lead). ... A grain is a unit of mass equal to 0. ... BIC pen cap, about 1 gram. ...

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 2260 feet 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 approach 6000 foot pounds of muzzle energy. Federal is now loading a 500 grain Barnes X bullet with a sectional density and ballistic coefficient that allows it to maintain approximately 2000 foot pounds of energy at 500 yards and a flatter trajectory that has never been even approached in this cartridge. Numerous companies offer rifles in this caliber, including the Winchester Model 70. 7mm magnum Winchester Model 70, with a muzzle brake. ...

The cost of these rounds are prohibitive, leading to a high number of handloaded cartridges. The recoil of the factory loads is about 70 foot pounds. Handloads can be made that will make this cartridge more comfortable to shoot. Handloading is the process used to create firearm cartridges by hand versus those put together en masse and sold commercially, generally in packages of 6 to 50. ... In physics, a foot-pound force (symbol ft·lbf or ft·lbf), usually abbreviated to foot-pound, is an Imperial and U.S. customary unit of mechanical work, or energy, although in scientific fields one commonly uses the equivalent metric unit of the joule (J). ...

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