Since they both use the 458 number are the 2 at all similar? I am only familiar with the 458 win mag not this 458 socom?

I just copied this directly from the Wikipedia article on the 458 SOCOM:

Inspired by the lack of power offered by the 5.56 NATO cartridge used in the M4 carbine and the M16 rifle, the .458 SOCOM came about from informal discussion of members of the special operations community, specifically Task Force Ranger's experience that multiple shots were required to neutralize members of the opposing force in Mogadishu during Operation Gothic Serpent. Marty ter Weeme designed the cartridge in 2000 and Tony Rumore of Tromix was contracted to build the first .458 SOCOM rifle in February 2001. Tony Rumore fired the very first round of .458 SOCOM ammunition in the Tromix shop located in Broken Arrow, Oklahoma on February 16, 2001, at 8:30pm.

The project sponsor set forth a number of specific requirements that led to the ultimate design as it stands right now[when?]: The cartridge had to fit in the M-4 carbine platform and magazines and be capable of firing heavy-for-caliber projectiles at subsonic velocity using suppressors. During the developments phase, various other cartridges were considered and proposed to the project sponsor, but rejected as not meeting all the requirements. The cartridges considered were 7.62×39mm M43, 9x39mm Grom, .45 Professional (which has since become the .450 Bushmaster), and .50 Action Express. At the time, the .499 LWR cartridge was still in development phase and had not been chambered commercially.

The .45 Professional was ruled out because in an interview with industry press, the developer of said cartridge stated that steel proprietary to General Motors was used in the bolts and extensions to withstand the high operating pressures. The .50 AE and .499 LWR were ruled out because in 2000 only two bullets were offered in .501 diameter, both developed as pistol bullets for the .50 AE and not heavy enough for the subsonic suppressed role. Research had indicated that a short belted cartridge called the .458 × 1.5" Barnes had been adopted for use in suppressed bolt action rifles for use in SE Asia during the Vietnam War. It was shown as effective in terms of ballistics, firing a 500 grain bullet subsonically, but not ideally suited for its role due to the size and weight of the platform. Combined with the wide selection of bullets available in .458 diameter, this cemented the choice of caliber.

The cartridge case design was finalized based on discussions with Tony Rumore at Tromix suggesting a lengthened .50 AE case would work well in the magazines as well as be the largest diameter case to be able to feed through the barrel extension. The rim size was chosen for compatibility with other platforms, primarily bolt action rifles, as the .473" diameter rim is arguably the most common rim size globally (all bolt actions chambered in 7.92×57mm Mauser, .30-06 Springfield or .308 Winchester share this rim size). The case length was chosen to be compatible with the Barnes 300-grain X Spitzer bullet. In 2009, Barnes developed a new bullet specifically for use in the .458 SOCOM, the 300 grain Tipped Triple Shock X, also known as the TTSX or TAC-X.

As noted above, the cartridge was designed to be 100% compatible with the M4 platform. This included the buffer, buffer spring, GI magazines, many aftermarket .223/5.56 magazines, and magazine well. In .223/5.56 caliber, cartridges stack in a staggered (double stack) fashion. However, with the much larger .458 SOCOM, rounds "single stack" without any modification to the standard GI magazine feed lips or follower, making it the most versatile and cost effective big bore offering in an AR-15 platform.

Today, .458 SOCOM rifles and complete upper halves are available from Rock River Arms and Wilson Combat. Barrels and bolts can be purchased from Southern Ballistic Research. Brass for hand loading is exclusively produced by Starline. Loaded ammunition is also manufactured by Southern Ballistic Research as well as a few small boutique shops.

.458 SOCOM: 300gr at 1,900fps
.458 Win Mag: 300gr at 2,600fps

.30-30 WCF and .300 Win Mag are both .30 --- but very different ballistically. Same with the two .458s. Of course, you can throw 5 or more .458 SOCOMs as fast as you can pull the trigger. Not sure if anyone ever made a .458 Win Mag semi...

Not if they've ever shot one. Has to be the hardest recoil I've ever felt in a civilian firearm. Also the 458 win mag is almost an inch longer than the socom.

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Minimize the variables

In the late 60s, I remember reading about a Browning BAR semi-auto rifle in .338 Win. Mag. being re-barreled for .458 WM, the 2 ctges having the same case head size. I believe Jacques Lott, of .458 Lott fame and a noted big bore rifle shooter, created this .458 BAR.

I had a .458 Win Mag a while back. It was the first centerfire rifle my youngest ever shot. He wanted to go shooting with us one Sunday. I'd just bought the thing and had only had it out once before. So we loaded it up and handed to my youngest to shoot. It was at a hill. My buddy was standing back and off to the side. I thought he was there to catch my son. He laughed and said no, he wanted to catch the rifle if it came loose! It didn't. The first time I fired it we were at an informal range. We had nothing along to use as a target, so the same friend who was going to catch the rifle if my son let go had a steel truck wheel in his pickup. He tossed it out on a sand hill about 75 yards away and told me to shoot it. It does have brisk recoil . And the soft nose bullet hit the wheel in a crease or fold in the steel. Just punched its way along, also drilling another hole toward the middle. Pretty impressive for me. Also that I hit the thing with the first shot.

OK, the Socom round is probably about like a .45-70 in speed and energy. Not so sure the AR platform handles heavy recoil as well as a long gun, bolt or lever. The fun part of the .458 is that you can load it with some pretty impressive bullets. Standard seems to be 405 or 510 grains. Someplace in my reloading stuff I have a whole bunch of cast 500 grain lead bullets. Heavy bullets tend to hurt your shoulder. Mine at least. And I also have some .458 bullets with Tungsten cores. They were sold long ago as solids for African dangerous game. Tungsten is right up there with DU in density, leaving gold behind as light weight, with lead not even in the game!

I just worry about the socom round and what kind of beating the AR will stand up to. The lower is a pipsqueak design. The M70 African uses all kinds of tricks like lugs in the stock to help withstand the recoil. Folks that rechambered and rebarreled lesser rifles to .458 discovered they pounded the stocks apart over time. I wonder how the AR can handle that. Especially the plastic actions.

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Dick Burg

I have killed several deer and pigs, a few coyotes, a turkey and a bobcat with a 458 SOCOM, in an AR15 with 300gr Remington, and Hornady HP bullets, and 325 Hornady LeverEvolution bullets.

It is very accurate, recoil is very mild and it kills very well.
Function has been 100%.