458 SOCOM XL is 458 SOCOM ammunition loaded beyond the AR15 magazine limit. Chattahoochee Munitions manufactures 458 SOCOM XL: a 650 gr Maker REX subsonic projectile, 2.035 inches long, loaded in standard 458 SOCOM brass to 2.802 inches overall for the CM7S bolt action and 2.790 inches for the CM10 semi-automatic. Because the long projectile sits farther out of the case, it gives back usable case capacity for powder. The chamber and the case are standard 458 SOCOM; “XL” names the projectile and the loaded ammunition.
What Does XL Mean in 458 SOCOM XL?
XL means extended length. It describes the projectile and the loaded round, not the chamber, the case, or the rifle. An XL cartridge uses ordinary 458 SOCOM brass and fires from an ordinary 458 SOCOM chamber. What changes is the overall length: the XL round is about half an inch longer than a 458 SOCOM cartridge that has to fit an AR15 magazine.
Chattahoochee Munitions firearms, barreled actions, and magazines on Terminal 458 are chambered in 458 SOCOM and configured for XL, meaning their actions and magazines accept and feed the longer round.
The AR15 Limit That XL Moves Past
458 SOCOM was designed in 2000 by Marty ter Weeme of Teppo Jutsu to fit the AR15. That choice fixed the cartridge’s maximum overall length at 2.260 inches, the length an AR15 magazine and magazine well accept. With a 1.575-inch case, that leaves only about 0.685 inch of room above the case mouth for the projectile.
Light and mid-weight bullets fit that envelope. A long, heavy bullet does not fit well: to stay under 2.260 inches it has to be seated deep inside the case, where it takes up the space that powder would otherwise use. The heavier and longer the bullet, the more case capacity the AR15 limit takes away.
How 458 SOCOM XL Reclaims Case Capacity
The XL configuration removes the AR15 length limit by moving the cartridge into firearms with longer magazines. The 2.035-inch 650 gr projectile can then be seated less deeply, so more of the case is left for powder. The table below compares how far the same projectile would sit inside the case at each overall length (calculated from a 1.575-inch case).
| Configuration | Cartridge overall length | 650 gr projectile inside the case | Case length left for powder |
|---|---|---|---|
| AR15 magazine limit | 2.260 in | About 1.350 in | About 0.225 in |
| XL, CM10 semi-auto | 2.790 in | About 0.820 in | About 0.755 in |
| XL, CM7S bolt action | 2.802 in | About 0.808 in | About 0.767 in |
At the AR15 limit, a 650 gr projectile would fill about 86 percent of the case length. In the XL configuration it fills about half, which is why Chattahoochee Munitions loads the 650 gr projectile only at XL length.
458 SOCOM XL Specifications
- Chamber and case: Standard 458 SOCOM, factory-new Starline brass
- Projectile: 650 gr Maker REX, solid copper expanding, lead free, .458 inch
- Projectile length: 2.035 in
- Overall length: 2.802 in (CM7S bolt action), 2.790 in (CM10 semi-auto)
- 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
- Twist rate: 1:10 (Chattahoochee Munitions barrels); Maker recommends 1:10 or faster
Which Firearms Can Fire 458 SOCOM XL?
XL ammunition needs an action and a magazine long enough for a 2.8-inch cartridge. It cannot run in an AR15 or a mini-action bolt gun, because neither accepts a round longer than standard 458 SOCOM. It needs a short action or the AR10 platform.
- CM7S bolt action: A Remington 700-footprint short action with a modified MDT metal AICS-pattern magazine, offered with 12.5-inch and 16-inch barrels and as the 12.5-inch CM7S with the PLACID OTB suppressor.
- CM10 semi-automatic: A large-frame AR10-pattern rifle with a lower receiver machined for the modified AICS-pattern magazine, offered with 12.5-inch and 16-inch barrels.
Each platform has its own load. The bolt action load is 2.802 inches overall and is not intended for the CM10. The semi-auto load is 2.790 inches overall with a propellant configuration that cycles the CM10.
The Magazine Configured for XL
A standard 458 SOCOM magazine is an AR15 magazine, and it cannot hold a 2.8-inch round. Chattahoochee Munitions modifies the MDT metal AICS-pattern magazine to hold and feed XL ammunition in both the CM7S and the CM10. The 458 SOCOM magazine holds 7 rounds and is configured for XL length only; it is not suitable for shorter, standard 458 SOCOM loads.
Why 458 SOCOM XL Is Subsonic
Short-barrel subsonic shooting is the core of what Chattahoochee Munitions does. A subsonic bullet is held below roughly 1,050 fps, so the way to carry more energy is to carry more weight. The 650 gr projectile that XL makes room for delivers about 1,473 ft-lb at the muzzle while staying below the speed of sound, even at 0°F, where sound travels about 1,051 fps. The full story is in 458 SOCOM subsonic, and the comparisons with AR15-length cartridges are in 458 SOCOM vs 450 Bushmaster and 458 SOCOM vs 45-70.
XL ammunition is meant to be shot suppressed. With subsonic ammunition, use an enclosed suppressor on both the CM7S and the CM10. On the 12.5-inch CM7S, the PLACID OTB over-the-barrel system wraps much of the suppressor around the barrel, so the suppressed rifle stays short. For barrel choice and practical distances, read 458 SOCOM barrel length and 458 SOCOM effective range.
Firearms and Ammunition Configured for XL
Chattahoochee Munitions manufactures complete factory firearms, barreled actions, ammunition, and magazines configured for XL ammunition:
- 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
- CM7S 458 SOCOM barreled action
See every configuration on Terminal 458.
458 SOCOM XL FAQ
What is 458 SOCOM XL?
458 SOCOM XL is 458 SOCOM ammunition loaded longer than the AR15 allows: a 650 gr, 2.035-inch projectile loaded to 2.802 inches (bolt action) or 2.790 inches (semi-auto). Chattahoochee Munitions manufactures it, along with the CM7S and CM10 firearms configured for it.
Who makes 458 SOCOM XL?
Chattahoochee Munitions manufactures the XL ammunition, the modified magazines that feed it, and the CM7S bolt action and CM10 semi-automatic firearms configured for it.
Is 458 SOCOM XL a different cartridge or chamber?
No. The chamber and the case are standard 458 SOCOM. XL names the longer projectile and the loaded ammunition.
Can 458 SOCOM XL be fired in an AR15?
No. An AR15 accepts cartridges up to 2.260 inches. XL ammunition is about 2.8 inches and needs a short action or an AR10-platform rifle.
Can I shoot standard 458 SOCOM ammunition in a firearm configured for XL?
The chamber is standard 458 SOCOM, but the Chattahoochee Munitions XL magazine is configured for XL length and is not suitable for shorter, standard 458 SOCOM loads.
Why load 458 SOCOM longer?
A long, heavy projectile seated to fit an AR15 takes up most of the case. Loading it longer seats the projectile less deeply and reclaims case capacity for powder.
What is the overall length of 458 SOCOM XL?
2.802 inches for the CM7S bolt action load and 2.790 inches for the CM10 semi-auto load. Standard 458 SOCOM is limited to 2.260 inches.
What is the heaviest bullet for 458 SOCOM?
Chattahoochee Munitions loads a 650 gr Maker REX at XL length. A projectile that heavy and long needs the XL overall length; at the AR15 limit it would fill most of the case.
Can bolt action and semi-auto 458 SOCOM XL ammunition be mixed?
No. The bolt action load (2.802 inches) is not intended for the CM10. Use the semi-auto load (2.790 inches) in the CM10.
What twist rate does 458 SOCOM XL need?
Maker recommends 1:10 or faster for the 650 gr REX. Chattahoochee Munitions 458 SOCOM barrels use a 1:10 twist, faster than the 1:14 common on AR15 458 SOCOM barrels. See 458 SOCOM twist rate.