Shoot’n, Fish’n ‘n’ Hunt’n

The .458 Winchester Magnum would have to be one of the most controversial big game cartridges ever!

Introduction:

First introduced in 1956, the .458 Winchester Magnum (.458WM) has been with us for over 60 years and, during that time, it has been the subject of a great deal of controversy, which continues to this day. Originally the 458WM was designed to replace the large British nitro express cartridges in a relatively inexpensive, mass produced bolt action rifle that most American hunters, who aspired towards hunting in Africa, could afford. That rifle was the pre-64, Winchester model 70 “African” model and it is a very well designed, controlled-round feed rifle that was ideal for hunting dangerous game. The pre-64 Model 70 has gone on to become one of the greatest sporting rifles in history and these rifles are still much sought after. Ironically, today, original pre-64, African models, in excellent to mint condition, can fetch higher prices than some of the double rifles that they were meant to replace!

Up to the introduction of the .458WM, and indeed to this day, it was generally accepted that the ideal cartridge, for hunting the dangerous game of Africa, was one of at least .450 calibre shooting a 500grain projectile at around 2150 f.p.s. This equated to a muzzle energy of around 5,000 ft/lb and it was no accident that most of the great British cartridges, the .450NE, .465NE, .470NE and many others, were designed to approximate this performance level. Even the mighty .416 Rigby approached this energy level although with only a 400 grain bullet but at higher velocities.

458WM Performance:

To some degree, the .458WM came close to matching the performance of the old British cartridges, but the performance figures, originally published by Winchester, were exaggerated and generally not achievable. Indeed, it is curious that Winchester thought that they could match the performance of the big nitro express cases with a case as small as the .458WM. I guess that this is a similar attitude to the designers of the short magnums that have proliferated in recent years but now seem to be in decline. Modern powders are not yet capable of overcoming the advantages of the older, larger cases, which can easily hold more powder and which operate at more sensible and safer pressures (when properly loaded, of course). The short magnums, and the .458WM can almost be considered the first of the short magnums, might come close in performance but they often fall short of matching the performance of their older and bigger brothers; unless the reloader is willing to risk firearm, life and limb with excessive chamber pressures.

So it was with the .458WM and Winchester soon had to reduce the advertised velocities to less than 2000 fps. However, the problems with the .458WM were not just because of the small case and there were problems caused by the powder used in the original loads, too. In addition, the original 510gn projectiles were not up to the task and would often deform badly and fail to penetrate adequately. These last two problems have been largely corrected, over the years, with modern powders and with the availability of premium projectiles. However, there is absolutely no way of overcoming the problem of the restricted powder space of this case. There are some advocates of the .458WM who claim that they can now achieve the original advertised performance of this cartridge but some of them are ‘playing with fire’ – literally!

Please don’t take this discussion out of context as I am not condemning the .458WM; it is still a good cartridge that, with the right ammunition and in the hands of a good shot, can “lay low the mighty beasts of the dark continent”. Even when loaded to lower, more sensible chamber pressures, the .458WM still exceeds the energy levels of the .375 H&H Magnum which, in most African countries, is the minimum legal calibre for dangerous game. However, the .458WM does not match or replace the classic nitro Express cartridges and it should not be asked to do so. To overcome the main limitation of the .458WM, that being the small case capacity, the only practical solution is to use a case with more capacity and that is why cartridges like the .450 Watts and .458 Lott came into being. In South Africa, the .458 Express 3″ was developed to get away from the small case capacity of the .458WM and to do it with South Africa’s SOMCHEM brand powders. These cartridges will be discussed in future articles.

The Big British Cartridges:

In respect to the large British cases, they were designed so that they could function with cordite, as the propellant, and that they would do so at quite low chamber pressures. This was important because cordite was fairly sensitive to temperature increases and, when used in the very hot and humid environments of Africa and India, chamber pressures could escalate quite alarmingly. High temperatures, and therefore high pressures, not only present the danger of the firearm blowing up but, when facing down an irate bovine, pachyderm or feline, even a case stuck in the chamber could be a death sentence. The British gun trade almost universally, and quite rightly, embraced the big case/low chamber pressure philosophy and we ignore their experience at our peril.

Today, we no longer use cordite, and our modern powders are less sensitive to temperatures (note the difference between less sensitive and insensitive because there is no such thing as a propellant that is insensitive to temperature – not even the Hodgdon/ADI powders as is sometimes believed!) but this does not mean that the value of the large British cases is now null and void. Indeed, those big cases can still be made to work beautifully with appropriate modern powders and at relatively mild pressures. The British philosophy, for the design of dangerous game cartridges, is still valid even though propellant technology has advanced considerably.

But I digress, so I will get back to the discussion of the .458WM.

Making the 458WM Better:

As I said, the .458WM is still a good and useful cartridge, just as long as the reloader does not try and make it the equivalent of the big nitro express cartridges or try and match the performance of some of the .458WM’s descendants. A premium 500gn projectile at around 2000fps, will still get the job done on big and dangerous game, so there is no need to tempt fate by loading beyond this level. Some ammunition manufacturers, and also many reloaders, have now opted to replace the 500gn bullet with a 465gn so that they can still achieve the desired 2150 fps but without pushing pressures too far. This puts the muzzle energy, of the 465gn load, at around 4700 ft/lbs, which is comparable to the energy level of the .416 Rigby. This muzzle energy is also well in excess of the .450/400 and .404 Jeffery, with original loads, and these cartridges generated just a bit over 4000 ft/lbs and both of them have excellent reputations for the taking of big and dangerous game.

In any discussion where velocities and muzzle energies of cartridges for dangerous game are considered, please remember that this is only part of the equation and that the design and construction of the projectiles is of immense importance. Indeed, poorly designed and constructed bullets will tend to fail even more alarmingly when velocities rise. If you cannot obtain the best quality, dangerous game projectiles, then reducing your .458WM loads might, in fact, make it perform better on game.

One important issue, that the .458WM reloader must be aware of, is the ambient temperature at the time of your load development and, subsequently, at the time of your hunt. Load development, with the .458WM, should always be done in summer or when you can elevate the temperature of your ammunition before shooting. To work up maximum loads, at winter temperatures, is to court disaster when you take those loads off to Africa or northern Australia. A safe, but maximum, load developed in winter will almost certainly exceed safe pressure levels when used in summer or when used in a hot climate elsewhere in the world. This principle is true for all ammunition but it is especially so with the .458WM because the case capacity is so limited.

Lots of 458WM Projectiles:

One nice feature of the .458WM, for plinking and range use, is that it performs very well with cast bullets and this can help reduce the cost of shooting and practicing with this large cartridge. Flinging expensive, premium game bullets down range at paper targets gets a little hard on the wallet. Yet, with a hard-cast, gas-checked bullet, of the correct size and design, you can duplicate factory ballistics at much reduced costs. This same load will also work very well in the hunting fields for lightly built, non-dangerous game, but should not be used for anything that can fight back.

If you are not into cast bullets, then another nice feature of any .458 caliber big game rifle, is that there is a very large selection of bullets available, from budget projectiles intended for the .45/70 up to, and including, the expensive premium hunting bullets.

If you want to hunt with your .458WM, then you have a fine hunting rifle for everything up to, and including, the big five – just remember that there are loading limitations imposed by the small case and attempts to match the performance of other .458 cartridges, might end in disaster!

In Part 2, to be published in the future, we will take a longer look at loads and shooting with the .458 Winchester Magnum.

Copyright © 2017 - Robert Pretty - Shoot'n Fish'n 'n' Hunt'n.