The AR-15 platform, including the M16 rifle and M4 carbine, is probably the most versatile and user-friendly family of firearms on the planet. Shooters can change every component on these firearms with relative ease, including calibers. One of the most significant changes with regard to caliber is going to a much larger round like the .458 SOCOM over the standard 5.56 NATO/ .223 Remington.
Introduction to .458 SOCOM vs. 5.56 x 45
While 5.56 NATO is a fine cartridge in its own right, a cartridge like .458 SOCOM can be a true game changer. As big as the cartridge is, it can easily fit in a slightly modified AR magazine and a standard AR lower receiver. The only other components that need to be changed are the barrel, bolt head, and the ejection port needs to be enlarged.
The .458 SOCOM cartridge was developed by Marty ter Weeme of Teppo Jutsu LLC after informal discussions with members of the U.S. Special Operations community in response to reports of poor performance of 5.56 NATO ammunition during the Battle of Mogadishu, part of Operation Gothic Serpent of Black Hawk Down fame. The search was on for a new round, in a much larger caliber, with a heavier bullet to take the place of the 5.56 NATO cartridge, particularly when used in short-barreled variants like the Mk18.
Several other cartridges, both existing and newly designed, were considered, but in the end the .458 SOCOM was born. The .458 SOCOM cartridge design was finalized by Marty at Teppo Jutsu LLC in 2000, with the first rifles chambered in .458 SOCOM debuting in 2001, built by Tony Rumore of Tromix. Marty then reached out to Buddy Singleton of SBR ammunition to produce factory loaded .458 SOCOM ammunition. SBR continues the development of the cartridge by conducting pressure/velocity testing and making advances in custom smokeless powder formulations specifically made of the cartridge.
The parent case of the .458 SOCOM is an untrimmed variant of the .50 Action Express cartridge. Due to bolt thrust limits on the AR15/M4 bolt lugs, similar to the .50 AE, the .458 SOCOM operates at chamber pressures no higher than 35,000 psi.
When it comes to magazines, the 458 SOCOM was originally designed to function in standard steel and aluminum G.I. 5.56mm magazines. All 5.56 magazines will work with the .458 SOCOM with the exception of Magpul P-Mags. These have a center divider in the front that can block the bullet path, although some customers have been able to use them successfully. A number of manufacturers offer dedicated .458 SOCOM magazines with the feed lips properly formed and a different follower in place. These .458 SOCOM magazines tend to be more reliable than most home conversions where the feed lips are not reformed properly, and which still use the standard 5.56mm follower. Lancer brand magazines have been found to have the best feeding reliability.
The .458 SOCOM is a very large round in comparison to the 5.56 NATO. Fortunately, with a dedicated 6,7 or 10-round magazine, the shooter may not have to worry as much about capacity restrictions. A standard 20-round 5.56 AR magazine can hold 6 or 7 rounds of .458 SOCOM. On a 30-round 5.56 AR magazine this number goes up to 10, which tends to fall just within the capacity limit even in more restrictive jurisdictions.
The .458 SOCOM obviously uses a much larger bullet, with a diameter of 0.458” or 11.63 mm, as opposed to 0.223” or 5.56 mm in the typical/original AR-15 platform. The overall case length for the .458 SOCOM is 40mm, which is not that different from the 45mm case length of the .223 cartridge.
Being formed from a lengthened .50 AE case and firing a .45 caliber bullet means that the cartridge obviously is necked down to accommodate the bullet diameter. The first factory ammo for the .458 SOCOM round was produced by SBR Ammunition.
Using .458” diameter bullets gives the shooter a variety of options, as this bullet diameter is the same as what is used to load 45-70 Government ammunition as well as several other cartridges. As of this writing, typical .458 SOCOM projectiles are available in bullet weights from 250 grains to 550 grains. Some shooters, however, produce their own projectiles (including casting) up to 600 grains. The heavier bullets are loaded to subsonic speeds and work great in conjunction with a silencer or suppressor.
Contrast this with the 5.56 NATO or .223 Remington cartridges which offer bullet weights from 45 grains to 77 grains. They are great for small game, or for firing a larger number of rounds in rapid succession, but in most instances can lack the optimal one-shot stop in terms of terminal ballistics.
Not intended as a long-range cartridge, the .458 SOCOM offers a relatively flat trajectory within 100 yards, making it ideal for a big-game hunting or as a self-defense round. As such, it has shown to be suitable for most law-enforcement uses as well. One should, however, keep in mind that the effective range for most shooters will be within 250 yards.
At 150 yards, the typical .458 caliber bullet drops about 5 inches from point of aim. At 200 yards this can be 15 inches and at 300 it drops over 50 inches. This has to do with the bigger bullet diameter and the heavier projectile losing speed. An experienced marksman can make shots at those ranges by holding over the target once the trajectory for a given load at a certain range is determined. Note that this may be affected by using a shorter barrel, particularly in versions shorter than 16 inches such as a pistol or short barreled rifle configuration.
The 5.56 NATO may have an advantage here with regard to range, but the smaller diameter bullet will lose energy, too. Albeit not as quickly as a round fired from a 458 SOCOM rifle.
As one could imagine, the .458 SOCOM round generates more recoil than a 5.56 NATO round. How much more recoil, however, is subjective. This is dependent upon barrel length, the weight of the rifle, and in some cases whether a specific muzzle device, adjustable gas block, or piston system is used.
An experienced shooter will know how to properly hold a rifle and shoot it to mitigate recoil as opposed to a novice. Likewise, a background in shooting bigger calibers or large rounds in general will impart a different response when asked how much recoil is felt.
It is reported to be quite a bit less than something like a .300 Winchester Magnum or even a .458 Winchester Magnum round, but well above that of a standard AR chambered in 5.56 NATO. Many shooters have compared it to a 12-gauge shotgun round. This is a relatively good comparison as the 12 Gauge delivers 27 pounds of free energy as opposed to 23 pounds for the .458 SOCOM round. By comparison, the 5.56 NATO generates only 4 pounds of free energy.
Due to the use of a heavier bullet, combined with lower chamber pressure, the average muzzle velocity for a .458 SOCOM round hovers around 1900 feet per second. As with recoil and trajectory this can change due to barrel length - a shorter barrel will produce less velocity than a longer one - and of course the bullet weight in question, as a heavier bullet will result in lower muzzle velocity.
Muzzle velocity of a 5.56 NATO round measures at an average of 3200 feet per second at the muzzle. So, it’s velocity is almost twice that of the .458 SOCOM round, but the bigger and heavier bullet of the .458 SOCOM delivers significantly more muzzle energy than the standard 5.56 NATO AR round:the .458 SOCOM round generates close to 2400 foot-pounds of muzzle energy as opposed to the 5.56 NATO’s 1200 foot-pounds of muzzle energy.
When it comes to ballistic coefficient, there is a dedicated formula that must be followed. It may be beyond the scope of this article to delve into the minutia of it, but it basically breaks down to how the fired projectile performs aerodynamically.
The diameter of the bullet, its weight, sectional density, muzzle velocity, and how it performs regarding gravity and wind drag all come together as part of this equation. While mostly used by long range shooters for much smaller calibers, it may still be applicable for the .458 SOCOM.
Ballistic Coefficient (BC) for the typical 5.56 NATO is around .304 to .307, whereas .458 SOCOM comes in at about .302. Different bullets and loads will change these numbers, but surprisingly both are comparable.
It is well established that .223 Remington or 5.56 NATO is a remarkable hunting round, suitable for small game and varmints such as coyotes and foxes. Several states, however, have banned its use on bigger game such as deer or hogs.
The .458 SOCOM, on the other hand, excels as a hunting round on medium to large game. Hunters have successfully taken bear, boars, and deer with this round at ranges inside of 250 yards consistently.
The round offers excellent energy and penetration with a heavy .458 caliber bullet. Most hog hunters consistently boast about one shot stops with the .458 SOCOM round, citing that it penetrates through thick layers of bone and fat like a hot knife through butter.
Some deer hunters have reported great success with the extra heavy bullets at subsonic speeds performing extremely well on deer at 250 yards. For this combination, however, you need to keep in mind the bullet’s trajectory and what we mentioned about the drop of the round when shooting at distances past 200 yards.
As it performs well on medium to large game animals, the .458 SOCOM will offer similar performance against two-legged predators. A suppressed .458 SOCOM with a short barrel will make for the ultimate home-defense or ranch defense weapon.
Afterall, this was the reason this round was originally developed. The project sponsors wanted a capable self-defense round for the military, to work reliably within 200 yards to stop an enemy soldier with one shot.
Likewise, an M4 carbine chambered in .458 SOCOM in the hands of a law enforcement officer would make for an excellent patrol rifle or carbine within its effective range. Different loads and different bullets make for a very diverse range of uses in the AR platform to include barrier and vehicle engagements.
With all that in mind
The .458 SOCOM cartridge has a lot to offer a shooter who hunts or is looking for a self-defense rifle or carbine with devastating potential against targets - be it game animals, paper targets, steel targets or dangerous attackers. For any of these, there is only one place to go for your .458 SOCOM needs: SBR Ammunition.
SBR Ammunition is the company that produced the first factory ammunition for .458 SOCOM. Our development is ongoing, and we offer ammunition for almost any scenario for use out of a .458 SOCOM rifle or carbine. We even offer stainless steel barrels to build your own .458 SOCOM rifle as well as various types of .458” diameter bullets so you can load your own ammunition.