photo © Wikipedia

(Note H110 & W296 are the same as of 2008 as is HP-38 & W231)
(IMR 4227 is same as H-4227 if made in Australia)

.458 SOCOM From Wikipedia, the free encyclopedia

(from Starline Brass) 458 SOCOM Brass (Large Pistol primer) 1.569"-1.576" O.A.L. A very popular cartridge, this 50AE based case contains a .308 style head configuration with O.A.L. of 1.575 necked down to accept a .458 dia. projectile. This case has been chambered in AR-15s and Bolt Guns. Dies are available from Hornady and Lee Precision.

5.56 NATO vs .458 SOCOM
Bullet weight/type Velocity Energy
250 gr (2,000 ft/s) 2,938 J (2,167 ft·lbf)
300 gr (1,900 ft/s) 3,261 J (2,405 ft·lbf)
600 gr (1,000 ft/s) 1,811 J (1,336 ft·lbf)

The .458 SOCOM is a relatively large round designed for a specialized upper receiver that can be mounted on any AR-15 pattern rifle. The 300-grain round offers a muzzle velocity 1,900 fps.

[edit] History Inspired by a supposed lack of power offered by the 5.56 NATO cartridge used in the M4 and the M16, 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, Inc was contracted to build the first .458 SOCOM rifle in February 2001.

The project sponsor set forth a number of specific requirements that led to the ultimate design as it stands right now: The cartridge had to fit in the M-4 platform and magazines, 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, 9×39mm 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 .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, Inc. 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 just above the rim is .538" in diameter. 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. (Thanks to Wikipedia for above paragraphs)

(Note: Many are near maximum loads, you should use 10% less to start.)
(See note on Powders below or read all about various Powders.)
Bullet is .458" diameter. Due to different barrel lengths, type of bullet, seating depth, primer type and other factors, you may not get near the FPS charted. It is just a guide and the reason you should start under these charges and work up.

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300 Barnes X
    Lil'Gun      32.8 gr.  1,886
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300 Remington JHP
    Lil'Gun      29.5 gr.  1,745
    Lil'Gun      30.5 gr.  1,788
    Lil'Gun      32.0 gr.  1,854
    Lil'Gun      34.6 gr.  1,985 (very hot load)
    H-110        34.8 gr.  1,645
    W-296        33.5 gr.  1,772
    H-4198       40.2 gr.  1,756
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325 Hornady  FTX
    IMR-4198     38.6 gr.  1,593
    H-4198       38.8 gr.  1,604
    Lil'Gun  (use between 28.5 gr. and 30.0 gr. for ~1,700-1,800 fps category)
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(note: Matt's Bullets makes a 365 Grain Lead, Round Flat Nose + Gas Check (.458)
     that should be experimented with if the flat nose does not create a feed problem)
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405 Remington JFP
    Lil'Gun      28.9 gr.  1,594
    H-110        34.4 gr.  1,657
    HS-6         14.5 gr.  1,086 (quiet with a suppressor)
    W-296        32.5 gr.  1,585
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420 Lead Cast RNFP + Gas Check
    Lil'Gun      28.0 gr.  1,602
    Lil'Gun      28.8 gr.  1,635
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500 Hornady RN
    IMR-4198     26.4 gr.  1,066
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