Taking a .458 SOCOM cartridge case and sizing the neck down to .375 caliber, resulted in a hard hitting AR-15 compatible cartridge, that has a considerable velocity and range advantage over the .458 SOCOM as well as other big bore AR-15 cartridges.
Typical .375 SOCOM loads will launch a 200 grain bullet 2400 feet per second from a 20" barrel.
In a short barrel suppressed subsonic application, the .375 SOCOM can be made to easily cycle the AR-15 action, using fairly fast burning propellants such as IMR 700X, Trail Boss and VV N32C (Tin Star).
.375 SOCOM head stamped brass is available from SBR Ammunition and reloading dies are available from Tromix, Redding, CH4D, Hornady, and Lee.
The .375 SOCOM feeds from most GI-type 5.56 M16 magazines, however Magpul P-Mags are not recommended.