Reloading The .458 SOCOM

Posted on: Wednesday January 6, 2021
.458 SOCOM brass
MD Smith

MD Smith




The .458 SOCOM

(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.

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

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.

300 Barnes X
Lil’Gun32.8 gr.1,886
300 Remington JHP
Lil’Gun29.5 gr.1,745 
Lil’Gun30.5 gr.1,788 
Lil’Gun32.0 gr.1,854 
Lil’Gun34.6 gr.1,985(very hot load)
H-11034.8 gr.1,645 
W-29633.5 gr.1,772 
H-419840.2 gr.1,756 
325 Hornady FTX
IMR-419838.6 gr.1,593
H-419838.8 gr.1,604

Lil’Gun (use between 28.5 gr. and 30.0 gr. for ~1,700-1,800 fps category)

(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)

405 Remington JFP
Lil’Gun28.9 gr.1,594
H-11034.4 gr.1,657
HS-614.5 gr.1,086 (quiet with a suppressor)
W-29632.5 gr.1,585
420 Lead Cast RNFP + Gas Check
Lil’Gun28.0 gr.1,602
Lil’Gun28.8 gr.1,635
500 Hornady RN
IMR-419826.4 gr.1,066

Discussion: * Most magnum pistol powders can be used as well as some rifle
powders. The somewhat faster pistol powders are preferable for the lighter 300
grain range bullets, while slower burning powders work better with the heavy
weights. However, case capacity can become an issue with bulky rifle powders.
If I can find some loads with 2400, that might be a good experiment.

Hodgdon’s Powder Guide on line and other internet sources. There is still a
lot of experimenting with loads and blogs as of 2012 are the best source. You
can back off loads. They may not work the action of the upper rifle, but you
can work up in .2 grain increments to find what is best.