.458 Winchester Magnum (using Sierra bullets)
Date: Mar 06 2019
The .458 Winchester Magnum was introduced by Winchester in 1956 in the Model 70 rifle. During this era, many of the big-bore, large-capacity cartridges of British and European origin were difficult to obtain ammunition for and the rifles were rather costly (and still are for that matter). The .458 Winchester was readily available from a domestic company, and the cost of rifles and ammunition were within the budget of most shooters. The cartridge became popular with shooters that wanted to experience the horsepower of a potent big-bore cartridge, but it also proved useful for hunters, guides and professional hunters that deal with large and potentially dangerous game. The cartridge is still in widespread use today.
Current factory ammunition has been reduced from early velocity claims, with Winchester’s latest catalog advertising a 510-grain soft-point bullet at 2,040 fps.
While the .458 case has body taper, it is handloaded similarly as straight-wall cartridges and requires a three-die set. After full-length sizing, the second die should be used to expand the case mouth just enough to allow the bullet to seat without damaging the case. Although some seat/crimp dies will allow the bullet to be seated and crimped in a single step, it is heartily recommended to first seat the bullet to its correct overall cartridge length then, as a second step, apply a heavy roll crimp. This method will not damage the case or the bullet and allows a heavy crimp to help keep bullets in place when cartridges in the magazine are subjected to heavy recoil.
The accompanying data for Sierra 300-grain bullets produced best accuracy using H-4198, IMR-4198 and IMR-4895 powders. A federal 210 Large Rifle Primer was used; however, the same data can be fired with large rifle magnum primers from Federal, CCI, Remington and Winchester.