The .45-70 is a mythically revered, legendary cartridge in American history. It’s famous for both hunting – most notably buffalo and bison – as well as its use as a military cartridge (it’s technically called the .45-70 Gov’t for good reason). It’s also one of the few cartridges that made the switch from blackpowder to smokeless powder, and is probably the most successful cartridge to make the jump.
But what if I told you it was possible to get similar capabilities from a modern firearm shooting a modern cartridge? I’m not talking about Marlin’s modern lever guns (as cool as those are). No, the round that makes that possible actually functions in America’s most popular rifle, the AR-15. It’s called the .458 SOCOM, and it was designed specifically to function within the AR-15 platform.
Military Might
Just like the origins of the .45-70 Gov’t, the .458 SOCOM has a fabled military history, though the modern round’s background is much more, well … modern. Most of us remember the infamous incident in Mogadishu, Somalia (for those non-history buffs, or those not alive for the incident when it happened, this conflict is depicted in the movie Black Hawk Down).
Rumor has it that the concept of the .458 SOCOM began at a barbeque involving a member of the U.S. Special Operations community while discussing the shortcomings of the 5.56 NATO round when used in the Mogadishu incident. The idea was simple: Make a round that fit in the standard M4 platform currently in use that also used all the current parts (mostly; the barrel would need to be changed), and make sure it hit like a brick. The cartridge’s inventor, Maarten ("Marty") Weeme, teamed up with Tony Rumore of Tromix (which makes many .458 SOCOM parts), and after modifying some .50 AE brass, the .458 SOCOM cartridge was born.
Big-Bore Benefits
You may be wondering what on earth was the idea behind putting such a big bullet in such a small cartridge? After all, the size of an AR-15 action and magazine restrictions only allow for extremely short cartridges. And you’d be right. The cartridge is extremely small, and normally, you’d want a big case to push a big bullet super-fast. But speed wasn’t the goal here. It was intended for the military, and when you want range, you go with a sniper round, anyway.
The .458 SOCOM was designed for short to medium engagements. Therefore, it doesn’t need to be pushed fast when the bullet doesn’t need to travel too far. And even when traveling slow by bullet standards – the .458 SOCOM’s standard 300-grain bullet is only trucking along at about 1,800 or 1,900 fps – it still carries about double the energy of the standard M4 round (to wit, the 5.56X45 NATO shooting a 55-grain projectile at the muzzle). Plus, unlike the 5.56, you truly can suppress a .458 SOCOM and keep velocities below the speed of sound, making the firearm extremely quiet—and perfect for hunting big game.
The do rounds feed from standard AR-15 magazines, too; capacity is roughly 10 rounds of .458 SOCOM in a typical 30-round AR-15 magazine. Though you take a hit on capacity, with those 10 .458 SOCOM rounds, a shooter gains nearly double the bullet weight, at 3,000 grains, or almost half a pound (there are 7,000 grains in a pound). Load the magazine up with subsonic rounds, like 500-grain .458 SOCOM ammunition, add one in the chamber, and congratulations, you now have more than ¾ of a pound in bullet weight with you. And that payload can be swapped out in a matter of seconds with a mere magazine change.
Load Up
The .458 SOCOM is a pretty niche round. A .458-caliber bullet, while common for a big-bore caliber, doesn’t mean much—most popular rifle calibers start with a 3 or less. That said, there are a few select ammo manufacturers out there who deal in .458 SOCOM. On MidwayUSA, there are 21 choices of ammo for the .458 SOCOM, from four manufacturers: Buffalo Bore (hottest-loaded ammo, mostly copper projectiles), Underwood (lowest cost), SBR (specializes in .458 SOCOM ammo manufacturing, and makes a popular powder for the cartridge, too), and HSM (one load specifically intended for hunting).
Ammo for the .458 SOCOM starts at about $45 per box (roughly $2.25 per round) on the low end, and go up to nearly $95 (about $4.75 per round). Cost all depends on the projectile selected.
If one wants to handload, the same projectiles loaded in those ammo offerings can be purchased, as well as a variety of others. That’s one nice thing about the .458-caliber bullet: It is the most common of the big-bore rifle bullets, largely thanks to the .45-70. For those curious, the lightest bullets come in at about 250 grains, while the heaviest .458-caliber bullets tip the scales at 550 to 600 in some cases.
A few words on bullet selection should be heeded. If you’re shooting an AR in .458 SOCOM, don’t shoot pure lead bullets, as the lead can cause issues with the gas port. Always use jacketed or solid-copper bullets.
Secondly, the .458 SOCOM (and .45-70 for that matter) needs to shoot .458 bullets specifically; no .452-caliber bullets should be used, as these are pistol bullets designed for cartridges like the .450 Bushmaster, .45 Colt, .454 Casull, .460 S&W Mag. and .45 ACP, among others. Any bullet you can load in a .45-70 case, you can load in the .458 SOCOM, too, while using much less powder to get nearly the same velocity.
This includes Hornady’s new SUB-X 410-grain bullet, which, if you’re a hunter, is ideal for subsonic hunting applications. The other bullet I highly recommend is the Barnes TTSX bullet made specifically for the .458 SOCOM, as it expands at a much lower velocity than most other monolithic bullets. I’ve shot the latter and got sub-MOA groups out of my Rock River Arms upper, and I’ve loaded up the 410-grain Hornady variants with Benchmark powder using Hodgdon’s subsonic reloading data. I’m just waiting on my 46 Banish suppressor from Silencer Central; no point in shooting rounds meant to be suppressed without, well, suppressing them!
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