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Interesting read, 458 SOCOM for AR upper

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/07/2010 at 13:38
Sgt. D View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire

Joined: February/20/2008
Location: North Carolina
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Points: 3836
I saw this on Military .com and thought some of you might see something you like.
Bookmark and Share Rifle Review:.458 SOCOM

by Ralph M. Lermayer

There are several ways new cartridges come into the world. One is the military. They put out a request for a set of specs they want, and arsenals and commercial manufacturers go into high gear until the round is created. The .308, .223, 7mm Mauser, and venerable .30-06 were all created this way.

Then, there are the guys in lab jackets at the commercial plants who try to bring out new commercial cartridges with a little more oomph and, hopefully, sales appeal. The recent rush of short and super-short cases that followed the .300 RUM are a perfect example of this, as are the .444 Marlin, .338 Federal along with many others.

Then, of course, you have the "wildcatters" who take everything out there and neck it up and down just to see what happens. Occasionally they hit a home run, and the likes of the .22-250, .257 Roberts, 6.5x284, or .224 TTH are born.

This cartridge, however, the .458 SOCOM (.458 Special Operations Command) was reportedly given birth over a barbeque and some cold brew. It was at an informal gathering of special ops personnel, specifically Task Force Ranger, when the subject of stopping power came up. It seems it took multiple hits to permanently take the opposition "out of the game" in Mogadishu, Somalia. The consensus was a one-shot stop would sure be nice. Marty ter Weeme, founder of a company called Teppo Jutsu, L.L.C., went to work. In 2000 a sledgehammer cartridge that would launch 250- to 600-grain .45 caliber bullets from a standard size AR-15 with a proper barrel and chamber was born — enter the .458 SOCOM.

A Bit of AR History

Back in the late '50s, the military decided to replace the venerable Garand. Most of the companies bidding for the new gun contract assumed another .30 caliber was the way to go, and the early designs submitted were in .30-06 or .308. ArmaLite's entry, called the AR-10, was a semi-auto of simple design (with a full-auto option) chambered in .308. As is often the case with government requests, about halfway through the trials, the higher brass decided the emerging dust-up in Asia would be a close quarter affair, and it might be better to abandon the bulkier, heavier .30 caliber and move to a smaller, lighter, faster round. That sent all the competitors who were bidding for the lucrative new rifle contract back to the drawing board.

ArmaLite engineers simply took their .308 AR-10, made it smaller, chambered and timed it for a new, hot .22 based on a blown-out .222 called the .22 Special, later named the .223, and resubmitted it as the AR-15. The rest is history. The Government bought it, Colt bought the design rights from ArmaLite, and AR-15s wearing a Colt logo tromped the rice paddies of Vietnam for years, going on to become the primary military firearm to this day.

Sounds Simple, But...

What does all this have to do with the .458 SOCOM? It's a size and timing thing. Because of the small size of the AR-15 action and receiver area, and the timing of the bolt cycle rate, you can't really use cartridges much longer in overall length than the .223 (a max of 2.26 inches OL). You can make a fatter case work, but you can't be very much longer. The pressure and burn rate must also be close to that of the .223 or timing goes to pot, you tear things up, and reliability suffers.

These were the design limitations Marty ter Weeme had to work around to give the little AR-15 real muscle, but it didn't stop there. The cartridge had to be suppressor-friendly, meaning it had to be capable of muzzle velocities below 1,000 fps (subsonic) and still reliably cycle the action in semi- or full-auto. That's a tall order.

The Case

The end result is a bit of an odd-looking case, but one that accomplishes all the goals. In short, a short, fat case (1.575) with a very small rebated rim (.473), minimal taper, and a slight shoulder. The case headspaces on that minimal shoulder (see drawing). It's an odd set of dimensions, but, as we will see, an extremely clever design for its purpose.

The Why Of It

In the world of bolt actions, levers, single-shots, and even handguns, hunters have an abundance of big-bore .45 caliber options to choose from, ranging from the .458 Winchester down to the .454 Casull. Big, heavy bullets moving at moderate velocities are proven game-stoppers when a fast stop is the vital objective.

The rising popularity of the AR-15 and its rapid move to the dark timber has generated a need for that kind of muscle in the AR. Other cartridges like the .450 Bushmaster or .50 Beowulf were created to fill this void. They are fine cartridges that get the job done, but they both require that the rifle be modified. Parts need to be changed to make them function. Buffer springs, unique magazines, different bolt, etc., are required.

The real cleverness in the design of the .458 SOCOM is that nothing but the upper need be changed — same magazine as the .223, same buffer spring in the buttstock, same everything. Just get a .458 upper available from Rock River Arms, Teppo Justsu, or other custom builders, get loaded ammo from SBR Ammunition, Corbon, or Reeds and go. Now, your .223 AR has morphed from a varmint getter to a full-fledged deer-, bear- and elk-stopper by simply changing the upper — no new FFL transfer required.

In The Field

Much of the research on the capabilities of big-bore AR-15 rounds like the .458 SOCOM concentrate in the area of subsonic (1,050 fps and lower velocities) and suppressed loads. That's the where and why of the super-heavy 450-, 500- and 600-grain bullets. I would imagine folks hiking, fishing or living in big bear country might also opt for the heavy weights. The Coast Guard uses them to put big holes in bad boats, but for hunters, bullets in the 250 to 350-grain range will be the most useful.

A 300-grain, well-constructed bullet moving at about 2,000 fps is 150- to 200-yard bad medicine for just about anything, including bear and moose. It's certainly big enough for elk, and there's not a deer alive that will walk away from a solid hit. The energy of such a combination is 2,400 foot-pounds at the muzzle and, within 100 yards, it doesn't weaken much. That puts it squarely in the territory of the modern .45-70 or .450 Marlin, and it will do anything those rounds will do. The mighty .458 Winchester Magnum only bumps 2,100 fps with the 300-grainers. 

Of course, all of these other cases soon outperform the .458 SOCOM as bullet weights get heavier since they have the case capacity to push the 400-, 500- and even 600-grain heavy weights much faster. With those weights, you don't have enough powder capacity in the .458. Velocity drops fast, and they slow way down and go subsonic, precisely as the design required.


Dies are available from Hornady,

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/07/2010 at 13:43
pyro6999 View Drop Down
Optics Retard
Optics Retard

Joined: December/22/2006
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you know i think dale clifford has one of these.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/07/2010 at 14:34
SVT_Tactical View Drop Down
Chief Sackscratch

Joined: December/17/2009
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Right now this is at the top of my list for my next upper
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/07/2010 at 18:54
Smokey53119 View Drop Down
Optics Apprentice
Optics Apprentice

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I shot one of these at the DU outdoors festival in 2007 or 2008.  I was an accurate little thumper.  Very cool to be sure.  Did have some feeding problems though.......
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