.458 SOCOM/ RRA LAR-458

.458 SOCOM/ RRA LAR-458

300 Whisper, .223 Rem, .458 SOCOM
L-R .300 Whisper, .223 Rem, .458 SOCOM

Rock River Arms AR platform chambered in .458 SOCOM


Caliber: .458 SOCOM
Barrel: 16” Chrome Moly Bull Barrel, 1:14 R Twist
Action: Semi-Auto AR Platform
Overall Length: 36”
Weight (empty): 7.6 pounds
Magazine: Standard .223 AR-15 Mags

SOCOM (Special Operations COMmand) contracted out for a new project which was brought on by a lack of power that the 5.56NATO cartridge has in the M4 and the M16.
SOCOM set a number of specific requirements for this new weapons system such as that the round must fit the standard M4 – M16 Platform and standard magazine and be capable of firing heavy-for-caliber projectiles at subsonic velocity using suppressors.

Marty ter Weeme, founder of Teppo Jutsu LLC. designed the cartridge in 2000 and Tony Rumore of Tromix, Inc was contracted to build the first .458 SOCOM rifle for use in February 2001.

In the developments phases, there were various other cartridges that were considered and proposed to the project sponsor, but rejected as not meeting all the requirements. The cartridges considered were 7.62x39mm, 9x39mm Grom, .450 Bushmaster, and .50 Action Express.

The .458 SOCOM uses the standard AR mag but due to it size does not allow for double stacking the rounds and subsequently only lets the mag hold a fraction of the rounds.

  • 10 rounds Magazine designed for .223 will hold 3 rounds of .458 SOCOM
  • 20 rounds Magazine designed for .223 will hold 7 rounds of .458 SOCOM
  • 30 rounds Magazine designed for.223 will hold 10 rounds of .458 SOCOM
  • 40 rounds Magazine designed for.223 will hold 13 rounds of .458 SOCOM
  • The 90-round .223 drum can hold as many as 33-36 rounds of .458 SOCOM
  • The 100 round beta mag will not work.

The AR-15 platform chambered in the .458 SOCOM gives a hunter a lightweight rifle with in  heavy caliber  that is durable and well suited for large game hunting.