.458 Winchester Magnum
Date: Mar 08 2013
The .458 Winchester Magnum was introduced by Winchester in 1956, first chambered in the Model 70 rifle. Timing was perfect, as many of the large bore British and European dangerous game rifles and cartridges were becoming hard to find and costly. The .458 was readily available from a large, domestic company, with rifles and ammunition costing considerably less. In the decades since, it has become popular and is chambered in many rifle configurations including variants of the bolt action, single shot and double guns. The .458 Winchester Magnum is widely used among hunters, Professional Hunters and guides that deal with large and potentially dangerous game.
The .458 is essentially a straight case with slight body taper, and thus requires a three-die set to handload. Full-length case sizing should be followed with just enough case mouth flaring to allow bullets to readily "start" and "seat" without damage to the mouth. Although some bullet/die combinations allow bullet seating and crimp to be accomplished as a single step, generally the (heavy) crimp should be performed as a separate step, which will help keep bullets in place when subjected to recoil.
When approaching maximum loads, it is especially important to check for signs of excessive pressure. During testing, we watched the pressure rise sharply to worrisome levels with several "maximum" loads, which were omitted from the accompanying data. Many double rifles will perform (in regard to accuracy and regulation) better with less stress to the action and hinge pin with loads that push 500-grain bullets to around 1,900 to 2,000 fps.
A Large Rifle Magnum primer is generally recommended; however, when using maximum charges of spherical powders that are compressed, to prevent hang-fires, it is especially important.