.375 SOCOM Subsonic

The .375 SOCOM is a niche but highly effective cartridge for subsonic shooting, designed specifically to provide large-caliber terminal performance in suppressed, low-velocity platforms, particularly in AR-15-style rifles. Based on the .458 SOCOM case necked down to accept .375 caliber bullets, this cartridge combines a generous case capacity with heavy bullet compatibility, making it well-suited for reliable subsonic performance.

One of the main advantages of the .375 SOCOM for subsonic use is its ability to stabilize and launch very heavy bullets — typically in the 250 to 350 grain range — at subsonic speeds (~1,050 fps or lower) without compromising on terminal energy. Projectiles like the 350gr Lehigh Defense Controlled Fracturing or 300gr Sierra MatchKing HPBT are popular choices among subsonic reloaders, offering both expansion and accuracy.

Because of the case’s relatively large internal volume, careful selection of fast-burning powders is necessary to avoid inconsistent ignition or pressure spikes. Common powders for subsonic .375 SOCOM loads include IMR 4227, Trail Boss, Shooters World Buffalo Rifle, and Hodgdon H110. Reloaders often fill to around 90–100% of case capacity with these bulkier powders to improve ignition uniformity.

A 1:10 or 1:8 twist rate barrel is recommended to ensure proper stabilization of long, heavy bullets at lower velocities. Additionally, since the .375 SOCOM was built with suppression in mind, it pairs extremely well with quality suppressors, producing a deep, low-register sound signature that is highly desirable for tactical or hunting applications.

Overall, the .375 SOCOM is a superb choice for shooters seeking subsonic performance with serious energy retention, especially in semi-automatic rifles. It’s ideal for medium-to-large game at close to moderate ranges, and it bridges the gap between traditional subsonic .30-caliber loads and the much larger .458 SOCOM in terms of both recoil and performance.