458 SOCOM subsonic ammunition fires a heavy .458-caliber bullet below the speed of sound, so a suppressed 458 SOCOM is quiet and still carries a lot of energy. Chattahoochee Munitions manufactures a 650 gr Maker REX subsonic load that averages about 1,010 fps from a 12.5-inch barrel with about 1,473 ft-lb at the muzzle. That projectile is too long for the AR15, so Chattahoochee Munitions loads it as 458 SOCOM XL and manufactures the CM7S bolt action and CM10 semi-automatic firearms configured to fire it.
Why Heavy Bullets Matter Below the Speed of Sound
A subsonic bullet has to stay below roughly 1,050 fps, so velocity cannot add energy. Weight can. At the same 1,010 fps, a 500 gr bullet carries about 1,133 ft-lb and a 650 gr bullet carries about 1,473 ft-lb, about 30 percent more. The .458-inch bore gives 458 SOCOM room for very heavy bullets, which is why it is a natural subsonic cartridge.
- Bullet: 650 gr Maker REX, solid copper expanding, lead free
- Velocity: About 1,010 fps from a 12.5-inch CM7S barrel (10-shot average)
- Muzzle energy: About 1,473 ft-lb
- Energy at 100 yards: About 1,342 ft-lb
- Ballistic coefficient: .44 G1
- Sectional density: .443
The AR15 Limit on 458 SOCOM Subsonic
458 SOCOM was designed to fit the AR15, which caps the cartridge at 2.260 inches overall. Heavy subsonic bullets are long, so at that length they have to be seated deep inside the 1.575-inch case, where they take up the space powder would use. The heavier the subsonic bullet, the more the AR15 limit costs.
458 SOCOM XL moves 458 SOCOM beyond that limit. The 2.035-inch, 650 gr projectile is loaded to 2.802 inches for the CM7S bolt action and 2.790 inches for the CM10, so it sits less deeply and reclaims usable case capacity. The chamber and the case remain standard 458 SOCOM.
Staying Below the Speed of Sound
A subsonic load must stay below the speed of sound in the conditions you shoot in, and the speed of sound drops as the air gets colder: about 1,116 fps at 59°F, about 1,087 fps at 32°F, and about 1,051 fps at 0°F. A bullet that crosses that line makes a supersonic crack downrange that no suppressor can remove. At about 1,010 fps, the Chattahoochee Munitions 650 gr load stays subsonic even on a 0°F morning.
Trajectory of the 650 gr Subsonic Load
Heavy subsonic bullets drop steeply, so range estimation matters. Chattahoochee Munitions calculated this table for the 650 gr load with a 100-yard zero. Read 458 SOCOM effective range for holds and practical distances.
| Range | Velocity | Energy | Drop | Time of flight |
|---|---|---|---|---|
| Muzzle | 1,010 fps | 1,473 ft-lb | – | 0.00 s |
| 100 yd | 964 fps | 1,342 ft-lb | 0.0 in | 0.30 s |
| 200 yd | 925 fps | 1,235 ft-lb | -35.9 in | 0.62 s |
| 300 yd | 891 fps | 1,146 ft-lb | -112.2 in | 0.95 s |
Barrel Length for 458 SOCOM Subsonic
A 12.5-inch barrel suits heavy subsonic loads. A subsonic load does not need a long barrel to reach its velocity, so a shorter barrel gives up little and keeps a suppressed firearm compact and well balanced. Chattahoochee Munitions tests its subsonic load in 12.5-inch barrels and offers both the CM7S and the CM10 with 12.5-inch barrels. A 16-inch barrel avoids SBR registration. Compare the two in 458 SOCOM barrel length.
Twist Rate for 650 Grain Subsonic Bullets
A slow bullet spins slowly, so long, heavy subsonic bullets need a faster twist to stay stable. AR15 458 SOCOM barrels are commonly 1:14. Maker recommends 1:10 or faster for the 650 gr REX, and Chattahoochee Munitions 458 SOCOM barrels use a 1:10 twist. CM7S barrels are made by Mos-Tek from 416R stainless steel. 458 SOCOM twist rate explains why the long bullet needs 1:10.
Bolt Action vs Semi-Auto Ammunition
Chattahoochee Munitions loads separate subsonic ammunition for each platform. Do not mix them.
- Bolt action: The 458 SOCOM subsonic ammo for bolt action is loaded to 2.802 inches for the CM7S and is not intended for the CM10.
- Semi-auto: The 458 SOCOM semi-auto ammo is loaded to 2.790 inches with a propellant configuration that cycles the CM10.
Both platforms feed from a modified MDT metal AICS-pattern 458 SOCOM magazine configured for XL length. It is not suitable for shorter, standard 458 SOCOM loads. Nothing cycles when the CM7S bolt action fires; the shooter opens the bolt after the shot, so the action adds no noise.
Suppressor Choice
458 SOCOM subsonic is meant to be shot suppressed. Use a suppressor rated for .458 caliber, and with subsonic ammunition use an enclosed suppressor on both the CM7S bolt action and the CM10 semi-automatic. On the 12.5-inch CM7S, the PLACID OTB over-the-barrel system wraps much of the suppressor around the barrel, so the suppressed SBR stays short.
Hunting With a Heavy Subsonic Bullet
A heavy subsonic bullet is a hunting bullet only if it expands at subsonic impact velocity. The Maker REX is a solid copper expanding bullet that Maker designs to expand at low velocity while holding its weight. With about 1,342 ft-lb at 100 yards and the steep drop shown above, 458 SOCOM subsonic suits suppressed hunting of feral hogs, whitetail deer, and bear at known, moderate distances. Read 458 SOCOM hunting and 458 SOCOM for bear, and see how the 650 gr load compares with a 395 gr subsonic in 458 SOCOM vs 450 Bushmaster.
Firearms Configured for the 650 gr Load
Chattahoochee Munitions manufactures complete factory firearms chambered in 458 SOCOM and configured for 458 SOCOM XL subsonic:
- CM7S 458 SOCOM 12.5-inch bolt action pistol or SBR
- CM7S 458 SOCOM 12.5-inch SBR with PLACID OTB
- CM7S 458 SOCOM 16-inch bolt action rifle
- CM10 458 SOCOM 12.5-inch semi-automatic SBR
- CM10 458 SOCOM 16-inch semi-automatic rifle
See every configuration on Terminal 458.
458 SOCOM Subsonic FAQ
Who makes 458 SOCOM subsonic ammunition?
Chattahoochee Munitions manufactures 650 gr Maker REX subsonic ammunition in 458 SOCOM, loaded separately for the CM7S bolt action and the CM10 semi-automatic, along with the firearms that fire it.
Is 458 SOCOM good for subsonic?
Yes. Its .458-inch bore accepts very heavy bullets, and weight is what carries energy below the speed of sound.
How fast is 458 SOCOM subsonic?
The Chattahoochee Munitions 650 gr load averages about 1,010 fps from a 12.5-inch bolt action barrel.
How much energy does 458 SOCOM subsonic have?
About 1,473 ft-lb at the muzzle and about 1,342 ft-lb at 100 yards with the 650 gr load.
What is the heaviest subsonic bullet for 458 SOCOM?
Chattahoochee Munitions loads a 650 gr Maker REX. It is 2.035 inches long, so it is loaded as 458 SOCOM XL beyond the AR15’s 2.260-inch limit.
Can 650 gr 458 SOCOM subsonic be fired in an AR15?
No. It is loaded to about 2.8 inches overall and needs a short action, such as the CM7S, or an AR10-platform rifle, such as the CM10.
Will 458 SOCOM subsonic stay subsonic in cold weather?
Yes. At about 1,010 fps, the Chattahoochee Munitions load stays below the speed of sound even at 0°F, where sound travels about 1,051 fps.
What twist rate does 458 SOCOM subsonic need?
Maker recommends 1:10 or faster for the 650 gr REX. Chattahoochee Munitions uses 1:10.
Can I shoot bolt action 458 SOCOM subsonic in a semi-auto?
No. The bolt action load is not intended for the CM10. Use the semi-auto load, loaded to 2.790 inches.
Should I use an enclosed or flow-through suppressor for 458 SOCOM subsonic?
Enclosed. With subsonic ammunition, an enclosed suppressor is recommended on both the CM7S bolt action and the CM10 semi-automatic.
Is 458 SOCOM subsonic good for hogs and deer?
Yes, at known, moderate distances. The 650 gr solid copper expanding bullet carries about 1,342 ft-lb at 100 yards.