458 SOCOM vs 300 Blackout: Extreme Semi-Auto Stopping Power

The 458 SOCOM and 300 AAC Blackout are two centerfire cartridges developed to increase the stopping power of the AR-15 platform. Both rounds were designed to work in a short barreled rifle (SBR) with a suppressor.

Adapting new cartridges to the AR-15 is nothing new, as the 6.5 Grendel, 6.8 SPC, and 224 Valkyrie have all been moderately successful. But none of these rounds can compare to the raw power that the heavier bullets of the 300 Blackout (BLK for short) and 458 SOCOM can bring to bear.

The 300 BLK and 458 SOCOM have the capability to fire supersonic and subsonic rounds with a simple upper receiver swap, lending a huge amount of flexibility to the platform. This leads many shooters to question which round is best for their next AR-15 build?

In this article, we will evaluate the 458 SOCOM vs 300 Blackout to help you understand the differences between the two and give you a clearer idea of which cartridge is best for your shooting needs.

What is the difference between 458 SOCOM and 300 Blackout?

The difference between the 458 SOCOM and the 300 Blackout is that the 458 SOCOM has a large case and fires a larger bullet. Although the 300 BLK is smaller, it uses a standard AR-15 bolt and magazine while maintaining its 30-round capacity while the 458 SOCOM has a 10-round capacity in standard AR mags.

Cartridge Specs

When evaluating centerfire cartridges, it’s a good idea to analyze the cartridge specs to gain more knowledge of each.

The primary chambering of the AR-15 platform is the 5.56 NATO, and although the round has many positive attributes which includes low recoil, low cartridge weight, and a favorable long range trajectory. Many shooters want a more powerful round for their AR-15 without having to upgrade to the AR-10. The 300 AAC Blackout and 458 SOCOM were both developed for the AR-15 to address the stopping power issue of the 5.56 NATO.

In general, the 300 BLK and 458 SOCOM both achieved their goals of increasing the overall power level of the AR-15 rifle, however the way each went about achieving it was somewhat different.

Developed in 2010 by the Advanced Armament Corporation (which was later acquired by Remington), the 300 Blackout was the brainchild of Robert Silvers who used a wildcat cartridge known as the 300 Whisper as the parent case for the 300 BLK. The goal was to replicate the terminal ballistics of the Russian 7.62x39mm round in the AR-15.

However, there were several additional criteria which needed to be met: the AR-15 standard bolt must be used, and the 30-round capacity needed to be maintained with standard NATO mags. Although other rounds like the 6.8 SPC and 6.5 Grendel were effective at increasing the lethality of the AR-15, they both required new bolts and specialized mags.

To date, the 300 BLK is one of the few rounds that successfully increased the kinetic energy potential of the AR-15 while only requiring a barrel change to perform a caliber conversion.

On the other hand, development of the 458 SOCOM began in 2000 in response to a conversation (supposedly at a barbecue) between Marty Ter Weeme of Teppo Jutsu LLC and a member of the United States Special Operations Command (SOCOM) surrounding the ineffectiveness of the 5.56 NATO round in the Battle of Mogadishu.

A 50 Action Express (50 AE) was lengthened to 1.575” and given a slight shoulder for the 458. The 50 AE is most well-known for being the primary chambering of the Desert Eagle handgun.

The 458 SOCOM is part of a classification of AR-15 rounds known as the Thumper Concept. The term was coined by American shooting icon Lt. Col. Jeff Cooper as he envisioned rounds that were 45-caliber or larger and capable of taking down a whitetail in a single shot.

The three most popular Thumper Rounds are the 450 Bushmaster, 458 SOCOM, and 50 Beowulf. To read more about these three rounds, check out this article: 450 Bushmaster vs 458 SOCOM vs 50 Beowulf.

Perhaps the largest, and most obvious, difference between the 458 and 300 is how massive the 458 SOCOM is next to the 300 BLK. The 458 has well over double the case capacity of the 300 BLK at 61.1 gr vs 26.5 gr.

However, this massive case capacity is needed for the massive 0.458” diameter bullets that the SOCOM round fires. The 300 BLK is no slouch when it comes to bullet diameter at 0.308”, but the 458 is simply bigger.

In general, 300 Blackout ammo will fire rounds between 110 and 265 grains for supersonic and subsonic muzzle velocities. The most popular supersonic bullet weights are 110, 125, and 147 grains while the most popular subsonic loads are 220 grain bullets.

The 458 SOCOM can fire heavier bullets between 200-600 grains, with the 250gr, 300gr, and 350gr factory loads being the most common.

Another case design difference is that the 300 AAC Blackout has a rimless case while the 458 has a rebated rim design, meaning their rim is narrower than their cartridge base. The 458 has a rim diameter of 0.473”, which is the same as the 308 Winchester, 30-06 Springfield, and 270 Win.

The 458 SOCOM case length is somewhat longer than the 300 BLK at 1.575” vs 1.368”, respectively. However, as both rounds are restricted by AR-15 magazine designs, their overall length of each round is the same at 2.26”.

Although it is the smaller of the two, the 300 BLK can handle considerably higher chamber pressures at 55,000 PSI per SAAMI specs.  At the time of writing, the 458 SOCOM is not currently certified by SAAMI so therefore it does not have a listed max pressure. Handloaders typically keep reloads below 35,000 PSI for the 458 but this number should not be considered a published maximum and you should always follow published load data when reloading for any cartridge.

Recoil

The 458 SOCOM has considerably more free recoil than the 300 Blackout.

Recoil is an important consideration when purchasing a new rifle as a round with heavy recoil will be more difficult to control and will slow your rate of follow up shots.

Free Recoil is affected primarily by muzzle velocity (FPS), powder charge, bullet weight, and firearm weight.

There’s a reason why the 458 SOCOM is called a Thumper Round, not only does it hit hard on large game, but the 458 imparts stout recoil on the shooter’s shoulder as well.

For this comparison we will analyze the 300 gr Barnes TTSX load by Buffalo Bore for 458 SOCOM and the 125 gr GameKing loaded by Sierra for 300 Blackout. We will assume the rifle weight is 7.5 pounds for a standard AR-15 carbine.

Given these bullets, the 300 BLK round will have 5.3 ft-lbs of free recoil compared to a whopping 25.4 ft-lbs of recoil for the 458 SOCOM. That’s almost a 5x difference between the two!

Muzzle Velocity, Kinetic Energy, and Trajectory

For this comparison we will analyze two different rounds for both cartridges. For the 300 AAC Blackout we will compare the 125 gr Sierra GameKing and Hornady 208 gr A-MAX factory loads. For the 458 SOCOM we will consider the Buffalo Bore 300 gr Barnes TTSX and Underwood Ammo 500 grain coated lead flat nose (FN).

These rounds were selected to compare the supersonic and subsonic loads for both 300 and 458.

When it comes to muzzle velocity, supersonic 300 BLK is about 200 fps faster than 458 SOCOM at 2,115 fps and 1900 fps, respectively. Subsonic loads are roughly equivalent in terms of muzzle velocity for both cartridges.

Where the two rounds really separate from each other is at range. At 300 yards the 125 gr GameKing load is still well above the speed while the 458 300 gr TTSX is approaching transonic speeds. For reference, the speed of sound in fps is 1,125.

Although the 458 SOCOM might not be the fastest round at the muzzle, it is packing a ridiculous amount of kinetic energy. The 300 gr TTSX Buffalo Bore load has a whopping 2,405 ft-lbs of kinetic energy at the muzzle compared to 1,242 ft-lbs for the GameKing bullet. That’s nearly a 2x difference!

The trend continues when comparing the subsonic loads, as the 500 gr 458 load has 1,283 ft-lbs of energy compared to 480 ft-lbs for the 208 gr Hornady A-MAX. To put this in context, the 300 Blackout subsonic round has around the same muzzle energy as a 45 ACP defense load.

The higher muzzle energy values for the 458 SOCOM give it a longer effective range when hunting large game like whitetail. The general rule found on whitetail hunting forums is that 1,000 ft-lbs is needed to ensure a clean kill on deer-sized big game. With this guideline, the 300 gr 458 can harvest a whitetail out to around 250 yards compared to just under 100 yards for the 300 BLK 125 gr load.

Although the 300 Blackout bows to the 458 SOCOM in terms of muzzle energy, the 300 BLK’s flat trajectory makes it a much better long range cartridge than the 458.

At 300 yards, the 125 gr 300 BLK round has -29.7” of bullet drop compared to -43.4” for the 458 300 gr TTSX. It is interesting to note that the trajectories for both subsonic rounds are almost identical despite the massive disparity in kinetic energy between the two loads.

What conclusions can we draw from these results?

The 300 Blackout was designed for both long range and short range shooting. The lighter, supersonic 300 BLK rounds have a considerably flatter trajectory than those for 458 SOCOM thanks to a higher muzzle velocity.

However, the 458 SOCOM hits considerably harder than the 300 Blackout at all ranges.

This showcases the different design concepts between the two rifle cartridges. The 458 was built for bone-crushing stopping power, while the 300 Blackout excels at being an intermediate cartridge that works well for long range shooting with adequate kinetic energy at shorter ranges.

Subsonic rounds for both cartridges are clearly for close range engagements, as they both have arching trajectories that would make a rainbow jealous.

Ballistic Coefficient and Sectional Density

Ballistic coefficient (BC) is a measure of how aerodynamic a bullet is and how well it will resist wind drift. Sectional density (SD) is a way to evaluate the penetration ability of a bullet based on its external dimensions, design, and weight.

Although there is a massive disparity in bullet weight between the 300 BLK and 458 SOCOM, the 300 Blackout is slightly favored in terms of ballistic coefficient. This is primarily due to bullet design, as 458 bullets tend to be short and wide, while 0.308” diameter bullets tend to be long and slender, making them more aerodynamic.

For 300 BLK, the 125 gr Sierra bullet has a BC of 0.318 compared to 0.236 for the 300 gr Barnes bullet.

Although 458 bullets are not extremely aerodynamic, they hit hard and penetrate deep giving them a slight advantage in sectional density over the 300 BLK.

The 300 gr TTSX has a SD of 0.204 compared to 0.188 for the 125 gr 300 Blackout projectiles.

Self-Defense/Home Defense

If you’re in the market for a self-defense carbine, then both the 458 SOCOM and 300 Blackout make exceptional choices.

One benefit of the 300 Blackout is that it was designed to experience a full powder burn in 9” of barrel length. Furthermore, subsonic 300 BLK rounds are completely hearing safe when combined with a suppressor.

A short barrel rifle (SBR) or even an AR pistol with a suppressor is a formidable home defense option combined with its inherent 30-round capacity of the 300 Blackout.

However, there’s no denying that the 458 SOCOM hits like a sledgehammer and leaves a substantially large hole than the 300 BLK. It’s also good to note that subsonic 458 loads typically have around 2.5x the kinetic energy of their 300 Blackout counterparts.

Although the 458 SOCOM is extremely powerful, one downside is the potential for over-penetration. In a home defense situation, over penetration is an extremely dangerous event where a bullet passes through the bad guy and hits an innocent bystander of family member.

As the 300 Blackout has substantially less kinetic energy, the potential for over penetration is lower (but not zero). Therefore, the 300 Blackout is our choice for home defense. Even though a big bore AR-15 in 458 is nothing any home invader would want to be on the business end of!

Hunting

The 458 SOCOM round makes an excellent option for close range big game hunting thanks to its powerful muzzle energy.

There’s no denying that the 458 has made a name for itself with whitetail hunters and elk enthusiasts alike, but hog hunting is where the 458 really shines.

The ability to take fast follow-up shots with a hard hitting round like the 458 makes it perfect for engaging multiple targets or making seconds shots on tough game like hogs. Feral pigs have become an increasingly large problem in the southern United States, as a herd of hogs can destroy an entire field in a single night.

This is not to say that the 300 Blackout is an ineffective hunting cartridge, as it has also made a splash in the deer and hog hunting communities. Many hunters prefer the lighter recoiling 300 Blackout over the heavier bullets of the 458 as lower recoil means even faster follow up shots.

However, the 300 Blackout is somewhat limited by its effective range of around 100 yards for deer.

It is NOT recommended to use subsonic 300 Blackout ammo for hunting medium game. These subsonic rounds simply do not have the muzzle energy or velocity needed for reliable expansion at hunting ranges unless otherwise specified by the manufacturer.

For varmint hunting, the 300 Blackout has more lightweight bullet options like the 110 gr Hornady V-MAX that are better suited for small game. However, for anything smaller than a coyote, you would be better served with a 223 Remington or 22-250 as these rounds are designed for this purpose.

To summarize, the 458 SOCOM is excellent for hunting big game like elk at close range. Both the 458 and 300 BLK can take on whitetail and feral hogs while the 300 is the better option for coyotes.

Ammo and Rifle Cost/Availability

When it comes to factory ammo and rifle availability, the 300 Blackout is clearly the best option.

As one of the most successful cartridges to be adapted to the AR-15 platform, the 300 Blackout has an incredibly loyal following in the shooting community. This popularity has spurned more ammo and rifle manufacturers to produce 300 BLK offerings to capitalize on the hype.

When it comes to ammo variety, the 300 BLK has approximately a 2:1 advantage over the 458 SOCOM. Manufacturers like Hornady, Winchester, Federal, Remington, Barnes, and Nosler all have 300 Blackout options available.

On the other hand, finding 458 SOCOM factory ammo can be a bit of a chore as it is considerably less popular than the 300. Most of your 458 ammo will come from custom manufacturers like Buffalo Bore, SBR, Black Butterfly, and Underwood Ammo.

In terms of price, cheap plinking ammo for 300 BLK runs around $1/round with premium hunting ammo fetching around $2/round with current market prices. On the other hand, 458 SOCOM ammo is considerably more expensive starting at $2/round for the cheap stuff and moving upwards to $5/round for the premium hunting ammo. Given these costs, it's always a good idea to purchase 300 Blackout ammo in bulk whenever possible to take advantage of lower per-round prices and ensure ample supply.

For rifle availability, both rounds benefit from the widespread popularity of the AR-15 platform as any of these rifles are a potential host for either cartridge.

Performing a caliber conversion on an AR-15 for 300 Blackout only requires a barrel change, as the magazines and bolt are the same as 5.56 NATO. A 458 SOCOM conversion requires a new barrel, bolt, and a single-stack magazine follower for standard AR mags.

Upper receivers for 300 Blackout are available in multiple barrel lengths and configurations from numerous manufacturers. Sourcing a 458 SOCOM upper receiver can be a little more tricky, as only a few manufactures like Tromix, Radical Firearms, and Bear Creek Arsenal currently have uppers in production.

If you’re looking for a bolt-action rifle, then the 300 Blackout is your only option as the 458 is offered exclusively in the AR-15. Several bolt-action rifles are available for 300 BLK, such as the Ruger American Ranch, the Remington 700 SPS Tactical, and the Savage Axis II.

Reloading

Reloading is one method shooters use to reduce their overall cost per round and increase the consistency of their ammo. Furthermore, handloads can be tailored to your specific rifle to meet your shooting criteria.

Both the 300 and 458 are excellent candidates for reloading. The 300 BLK is an excellent choice as components are readily available while the 458 is a good choice as factory ammo can be hard to come by at times.

The 300 Blackout fires the incredibly popular 0.308” diameter bullet fired by cartridges like the 308 Winchester, 30-06 Springfield, 300 Win Mag, and 300 WSM. Factory new brass can be had from multiple manufacturers; however, 5.56 NATO brass can be converted to 300 Blackout relatively easily if you know what you’re doing.

The 458 SOCOM fires the bulky 0.458” diameter bullet also used by cartridges like the 458 Winchester Magnum, 45-70 Government, and the 458 Lott. However, the bullets used by these other cartridges are typically longer than what is needed for 458 SOCOM ammo due to the overall length restrictions of the AR-15.

Therefore, finding bullets for the 458 SOCOM can be trickier than finding bullets suitable for 300 Blackout.

To make things more complicated, 458 SOCOM brass is more difficult to locate. Although the 458 descended from the 50 AE case, normal 50 AE brass cannot be swaged into 458 SOCOM cases. This is because elongated 50 AE cases were used to create the 458 SOCOM and adding brass to a case is incredibly complex.

This means that 458 handloaders are limited to factory new brass or saving their previously fired brass.

Final Shots: 300 Blackout vs 458 SOCOM

The 300 AAC Blackout and 458 SOCOM are two rifle cartridges that have successfully increased the stopping power of the AR-15.

The 300 Blackout offers shooter tons of versatility in bullet weight and barrel lengths. Undoubtedly one of the most popular cartridges offered in an AR-15 not named 5.56 NATO or .22LR, the 300 Blackout allows shooters a round that can be used for plinking as well as varmint and deer hunting.

The best part about the 300 Blackout is that it only requires a barrel change in an AR-15, as the 5.56 NATO mags and bolt can be used for 300 BLK. Furthermore, supersonic and subsonic ammo is available for complete shooting versatility.

However, if you want raw stopping power, it’s hard to beat the sledgehammer that is known as the 458 SOCOM. The mighty 458 was built around the concept of taking down a deer in a single shot in an AR-15 rifle.

The 458 offers insane kinetic energy values and is offered in both supersonic and subsonic ammo.

Most shooters will opt for the 300 Blackout, as it has lower recoil, ammo is more plentiful and less expensive, and reloading components are easier to find.

However, if you are a recoil junkie or just simply love firing a massive bullet out of your AR-15, then the 458 SOCOM might be the round you’ve been looking for.

No matter which cartridge you choose, make sure you stock up on ammunition here at Ammo.com and I’ll see you on the range!