Updated .458 Win Mag Load Data with New Components

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Introduced in 1956 as a low-cost answer to the expensive British Nitro Express dangerous-game cartridges, the .458 Winchester Magnum quickly gained a reputation for getting people killed. By elephants, generally. Why? Initial velocities advertised with 510-grain bullets were quite impressive—2,150 fps out of a 26-inch rifle barrel. That compared favorably to the classic, proven .470 Nitro Express, which produced 2,125 fps with a 500-grain bullet. In fact, it actually outdid it, as well as the .450 NE, .500/465 NE, and so forth.

When tested on U.S. ranges with fresh ammo, the .458 Win. Mag. performed as advertised. Unfortunately, the cartridge had a built-in weakness. Its case was designed short (2.50 inches) so that loaded cartridges would fit into .30-06-length actions (COL: 3.340 inches). That meant powder capacity was severely limited. Powders of the era had to be heavily compressed in order to achieve the touted velocity.

When subjected to a few years in wildly fluctuating climatic conditions in Africa (cold, heat, humidity), the heavily compressed spherical powder granules inside would clump up and greatly reduce ignitability and burn rate. So much so that reports of fizzing lumps of powder plopping out the end of one’s barrel came rumoring down the grapevine.

Naturally, this reduced bullet velocity. There were allegedly reliable reports of .458 bullets literally bouncing off elephants’ foreheads—a decidedly concerning outcome when face to face with a large, irate pachyderm. Obviously, those occurrences were rare, and if and when they did occur were squib loads caused by powder that failed to burn properly. In such cases the bullets must have exited the muzzles with only a few hundred fps of velocity.

Within a decade or two a bit of stigma hung over the .458 Win. Mag. cartridge. Even so, thanks to its affordability and ready availability in reliable bolt-action Winchester Model 70 rifles, the .458 Win. Mag. Model 70 became the unofficial standard-issue arm of many wildlife-control officers across Africa as well as outfitters and guides who couldn’t afford an English double-barreled express rifle.

Once again, note that when the ammunition performed as it was designed to, the cartridge actually hit harder than the .470 Nitro Express, which is saying something. Seems impossible, right? How can a low-cost, short .458 cartridge designed for bolt-action rifles measure up to the grand .470 Nitro with its long, tapered case; imposing frontal diameter; and legendary stopping ability? It’s all in the details, folks. Let’s take a closer look.

All in the Details

For starters, 510-grain, 0.458-inch-diameter bullets have extraordinary sectional density. (In bullets of like construction, sectional density is a measure of penetrating capability.) It’s a number derived via a formula based on bullet weight and diameter. Sectional density of a 510-grain, .458-caliber bullet is .347.

In a world where a sectional density number of .300 is the gold standard on which dangerous-game professional hunters are willing to stake their lives, a 15 percent increase is significant. When fired at advertised velocity, those 510-grain .458 Win. Mag. bullets penetrated like depth charges. For contrast, the 500-grain 0.475-inch-diameter bullets fired from the .470 NE have a sectional density of .317. That’s admirable, but it’s still 10 percent less.

Another allegedly superior advantage of the .458 Win. Mag. was its advertised muzzle velocity of 2,150 fps out of a 26-inch barrel, which, as noted, was faster than the .470 NE’s 2,125 fps. Kinetic energy generated by the 510-grain bullet at that speed is 5,236 ft-lbs. The .470 NE’s 500-grain bullet at 2,125 fps produces 5,014 ft-lbs. More energy. Deeper penetration. What’s not to like?

Unfortunately, the .458 Win. Mag. had demons, and the .470 NE did not. Occasional squib loads can be a literal death knell to hunters who walk among deadly game on a daily basis. No doubt, fervently wishing they’d based the .458 Win. Mag. on the full 2.850-inch length of the .375 H&H parent cartridge case rather than shortening it, ammo engineers scrambled to solve the issues caused by heavily compressed powder.

Various ammomakers reduced advertised velocity to somewhere between 1,950 and 2,060 fps. Loaded more lightly, powder charges were less compressed and less likely to solidify into hard clumps or cylinders that resisted ignition.

The standard bullet weight was reduced to 500 grains (which at 0.341 still provides a best-in-class level of sectional density), and in some cases to the 480-grain bullet standard in the .450 Nitro Express. Lighter bullets result in shortened bullet shanks, which opened up propellant capacity and further decreased propellant compression. Over time, more compact powders with appropriate burn rates for the .458 Win. Mag. were developed. And they were more resistant to clumping when under compression.

Bullets, too, underwent significant R&D. A short-lived but terrific nonexpanding .458 Win. Mag. bullet was the Speer African Grand Slam Tungsten-Core Solid, which was a 500-grain bullet with—you guessed it—a tungsten core. Since tungsten is heavier than lead, these bullets were considerably shorter than standard 500-grain .458s. This opened up a considerable amount of powder capacity inside, allowing .458 Win. Mag. cartridges to contain more powder with less compression. The result? Top-notch velocity without the risk of clumped, hard-to-ignite powder.

Unfortunately, the Grand Slam Tungsten didn’t last. Tungsten is too expensive, and sales of the very costly projectile didn’t support continued production. Bullet evolution in the monometal world had the opposite effect on projectile length. Being of a lighter-weight material than lead, all-copper and copper-alloy bullets are longer than their lead-core counterparts. Seating a 500-grain monometal bullet into a .458 Win. Mag. case eats up valuable powder capacity.

Still, such bullets not only survived, but they thrived. Because they lose virtually no weight when they mushroom, monometal bullets penetrate out of proportion to their weight. This enabled manufacturers to engineer .458 bullets lighter than traditional standards and still maintain reliable buffalo-killing penetration.

For example, Barnes now loads a 450-grain TSX in its standard .458 Win. Mag. factory ammo, which achieves 2,227 fps in the 24-inch barrel of my Model 70 Safari Express rifle. That bullet has a sectional density of “just” .306, which is nearly identical to the sectional density of standard—and legendary—300-grain .375-caliber dangerous-game bullets. Enough said.

Another example is Hammer Bullets, a newer, trendy monometal bullet company that offers several different 0.458-inch-diameter projectiles of between 402 and 447 grains. By all accounts, such bullets perform splendidly on dangerous game. In fact, although lighter, these monometals penetrate as well as and sometimes better than traditional 480- to 510-grain lead-core dangerous-game bullets. Why? Again, they usually shed little to no weight on impact. The lead core in a traditional bullet erodes away as the bullet penetrates, exponentially lightening the bullet and reducing its penetrating ability.

Monometal bullets proved so capable that bulletmakers began engineering similar-weight bonded-lead-core dangerous-game bullets for the .458 Win. Mag. For example, you can purchase 400- and 450-grain Swift A-Frames in addition to the classic 500-grain versions. These are debatably better for coastal brown bears and African lions than they are for Cape buffalos and elephants, but they’re proving superbly effective for certain purposes.

I recently had the opportunity to test several different updated .458 Win. Mag. factory loads in my Model 70 Safari Express. They are loaded with modern clump-resistant propellants and a variety of different modern bullets. Velocity performance is impressive. Check out the results in the accompanying chart.

Modern .458 Win. Mag. Handloads

Thanks to modern powders, handloaders can now achieve historically optimistic velocity without issues. I was first introduced to the outstanding potential of modern .458 handloads by world-class custom gunsmith Joe Smithson, who showed me a lovely rifle built on a 1909 Mauser action. Although too light (about nine pounds) to sufficiently tame recoil to the point where the average shooter can fire it comfortably, it’s perfect for a PH who may carry his .458 Win. Mag. 200-plus days a year.

Enthusiastically, Smithson stated, “We’re getting an easy 2,150 fps with 500-grain Hornady DGX bullets handloaded over Accurate 2230 powder…and that’s not a compressed load.” 

According to Smithson, Accurate 2230 powder is ideally suited for the .458 Win. Mag., as it achieves high levels of velocity without much (if any) compression. Joe suggested it enables the cartridge to be all it can and should be. As he put it, there’s little need for the longer .458 Lott when handloaders can achieve such performance with the .458 Win. Mag.

Another good propellant is Ramshot TAC, which typically provides top-tier velocities with acceptable levels of compression. Also, Alliant Reloder 7 is very good for bullets in the lighter weight ranges.

To work out a few modern propellants with modern bullets, I ordered a handful of different monometal 0.458-­inch-­diameter projectiles suitable for Win. Mag. speeds and picked up canisters of Accurate 2230, TAC, and Reloder 7. Knowing monometal bullets pose the greatest case-capacity challenges to the .458 Win. Mag., I focused on seeing what sort of velocities I could achieve with such bullets and minimal powder compression.

Exact load recipes are shown in the chart. I made a point of keeping powder compression to a couple tenths of an inch or less. By perusing a half-dozen different load manuals, as well as several online data sites provided by bullet and/or powder manufacturers, I did my best to choose propellants that would provide optimal velocity with the various bullet weights I had on hand.

With a magnum-thickness PAST recoil pad installed on my shoulder (I’m too old to cowboy up when shooting a lot of heavy-recoiling ammo), I set to work. Because of that substantial recoil and because I was primarily interested in testing velocity rather than measuring accuracy (which varies depending on individual rifles), I opted to fire just one, five-shot group per load.

I confess I was surprised to find I could achieve 2,165 fps even with 500-grain monometal bullets. It’s worth noting that not all monometal bullets are created equal in terms of velocity potential. Some pose less resistance in the bore, resulting in lower pressure peaks and enabling handloaders to drive them a bit harder. Barnes’s Banded Solid is notably easy to load for great speed. In contrast, the all-copper 500-grain .458 TSX expanding bullet by Barnes has more in-bore drag and is harder to push to high velocities.

However, using Accurate 2230 powder I was able to surpass that magical 2,150 fps threshold with the 500-grain Solid and the 500-grain TSX. For those interested, my 2,165 fps handloads generate 5,200 ft-lbs of kinetic energy. Without question, a dual-load pairing of 500-grain monometal expanding and nonexpanding solid projectiles is as versatile as dangerous-game loads can be—ideal for everything from crocodiles to Cape buffalos to elephants.

In the mid-weight projectile range, speeds of 2,250 fps are quite easily achievable with 450-grain bullets, and such loads have noticeably lighter recoil. Don’t expect them to shoot to the same point of impact as heavier 500-grain bullets, though. My Model 70 put a couple of the light-bullet loads eight inches higher at 100 yards.

How about light-for-caliber .458 bullets? Individual five-shot groups are no real test of accuracy, but it’s worth noting that my Model 70 (which is not a particularly accurate rifle with traditional .458 Win. Mag. factory loads) produced sub-MOA groups with both of the Hammer bullets I tested. For Alaska guides and coastal brown bear hunters, Hammer’s 404-grain Stone Hammer bullet is an excellent choice. It exits the muzzle of my Model 70 at about 2,530 fps and produced a one-inch five-shot group at 100 yards. Energy at the muzzle is an impressive 5,740 ft-lbs.

For .458 Win. Mag. rifle owners who want to use their big-bore gun on nondangerous game in America or on plains game species, a lead-core 350-grain bullet at about 2,500 fps is terrific. My custom knifemaker buddy Evan Siembida hunts whitetails with Speer 350-grain Hot-Cor bullets loaded over H322 powder, and in his words, it’s “…absolute hell on whitetails. Like flipping off a switch!”

Although the classic .458 Win. Mag. was once the practical man’s preferred choice for use on really big game across much of Africa, there are so many more exotic and even more practical choices today that it’s been overshadowed. However, the .458 Win. Mag. is better now than it’s ever been. Modern powders and advanced projectiles enable it to perform as well as originally advertised, and it actually achieves new levels of speed and downrange authority, all in a svelte .30-06-length action.

Nearly 70 years after its birth, the .458 Winchester Magnum has come into its own. 

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