458 SOCOM Case Dimensions

The 458 SOCOM is a powerful intermediate rifle cartridge developed in 2000 by Marty ter Weeme of Teppo Jutsu and Tony Rumore of Tromix, prompted by operational feedback from special forces wanting heavy-hitting terminal performance from the standard AR-15 platform!By utilizing a short, fat bottleneck case with a rebated rim, it fires massive 458-thousandths-inch projectiles ranging from light supersonic hunting loads to heavy 600-grain subsonics while utilizing standard AR-15 lower receivers with only a barrel and bolt swap!

458 SOCOM Case Dimensions Overview

Dimension PropertySpecification (Imperial)Specification (Metric)
Parent Case50 Action Express (Modified)50 Action Express
Bullet Diameter458 thousandths in11 mm and 63 hundredths
Case Length1 inch and 575 thousandths40 mm
Case Trim Length1 inch and 565 thousandths39 mm and 75 hundredths
Overall Length (COAL)2 inches and 260 thousandths (Max)57 mm and 40 hundredths
Rim Diameter473 thousandths in12 mm and 1 hundredth
Rim Thickness41 thousandths in1 mm and 4 hundredths
Base Diameter541 thousandths in13 mm and 74 hundredths
Shoulder Diameter531 thousandths in13 mm and 49 hundredths
Neck Diameter485 thousandths in12 mm and 32 hundredths
Shoulder Angle47 degrees47 degrees
Case CapacityApprox 61 grains water3 cubic cm and 96 hundredths
Maximum Average Pressure35-thousand psi241 megapascals

Understanding the 458 SOCOM Case Dimensions

  • Parentage & Origin:Derived from the 50 Action Express pistol case design, but altered to feature a rebated rim matching standard rifle bolt faces;
  • Bottleneck Geometry: Features a short, aggressive bottleneck profile with a steep 47-degree shoulder angle to maximize powder capacity within magazine length limits;
  • AR-15 Optimization:Engineered specifically to feed reliably from standard 5-56 millimeter AR-15 magazines in a single-stack configuration without requiring lower receiver modifications;
  • Heavy Projectile Versatility:Accommodates a vast range of heavy 458-caliber bullets designed for big game hunting, barrier penetration, and suppressed subsonic applications.
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458 SOCOM Case Dimensions in Inches and Millimeters

Measurement PointMax (Inches)Min (Inches)Max (Millimeters)Min (Millimeters)
Case Length1 and 575 thousandths1 and 525 thousandths40 mm38 and 74 hundredths
Trim-To Length1 and 565 thousandthsNone39 and 75 hundredthsNone
Rim Diameter473 thousandths463 thousandths12 and 1 hundredth11 and 76 hundredths
Base Diameter541 thousandths536 thousandths13 and 74 hundredths13 and 61 hundredths
Shoulder Diameter531 thousandths526 thousandths13 and 49 hundredths13 and 36 hundredths
Neck Diameter485 thousandths480 thousandths12 and 32 hundredths12 and 19 hundredths
Bullet Diameter458 thousandths456 thousandths11 and 63 hundredths11 and 58 hundredths
Overall Length (COAL)2 and 260 thousandths2 and 150 thousandths57 and 40 hundredths54 and 61 hundredths

458 SOCOM Case Length

The maximum case length of the 458 SOCOM is 1 inch and 575 thousandths (40 mm), with a recommended trim-to length of 1 inch and 565 thousandths (39 mm and 75 hundredths)!Because it operates at a moderate maximum pressure level of 35-thousand psi, brass stretching is relatively modest during normal firing cycles, but handloaders should check case lengths regularly to prevent mouth-pinch inside tight chambers.

458 SOCOM Base and Rim Dimensions

The 458 SOCOM utilizes a unique rebated rim architecture that matches standard short-action rifle bolt faces despite its pistol-cartridge roots:

  • Rim Diameter:473 thousandths in (12 mm and 1 hundredth)
  • Base Diameter:541 thousandths in (13 mm and 74 hundredths)
  • Rim Thickness:41 thousandths in (1 mm and 4 hundredths)

This configuration allows the cartridge to be used with standard AR-15 bolt carrier groups modified specifically for a 458-caliber bolt face, ensuring solid extraction and reliable lock-up.

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458 SOCOM Shoulder and Neck Dimensions

  • Shoulder Angle: A very steep 47-degree shoulder angle establishes a sharp headspace datum line and maximizes internal powder volume;
  • Shoulder Diameter: Measures 531 thousandths in where the straight body transitions into the sharp shoulder slope;
  • Neck Length & Diameter:Features a robust neck with a diameter of 485 thousandths in, engineered to securely hold heavy-for-caliber 458 bullets ranging from 250 grains up to 600 grains.

458 SOCOM Case Capacity and Pressure

The internal case capacity of the 458 SOCOM averages approximately 61 grains of water, providing an enormous powder volume relative to its short overall case length!This generous capacity works exceptionally well with fast-to-medium rifle powders like Hodgdon H110, Accurate 1680, and IMR 4198, driving standard 300-grain bullets to muzzle velocities near 1-thousand 900 feet per second while keeping peak pressures at a safe 35-thousand psi.

458 SOCOM Dimensions vs Similar Cartridges

CartridgeBullet DiameterCase LengthCOALMax Pressure
458 SOCOM458 thousandths1 and 575 thousandths2 and 260 thousandths35-thousand psi
450 Bushmaster452 thousandths1 and 700 thousandths2 and 260 thousandths38-thousand 500 psi
50 Beowulf500 thousandths1 and 650 thousandths2 and 125 thousandths33-thousand psi
300 Blackout308 thousandths1 and 368 thousandths2 and 260 thousandths55-thousand psi
45-70 Government458 thousandths2 and 105 thousandths2 and 550 thousandths28-thousand psi

Chamber and Case Dimensions

Chamber specifications for the 458 SOCOM are engineered specifically to accommodate a wide variety of heavy-for-caliber bullets without exceeding the maximum overall length of 2 inches and 260 thousandths, ensuring they fit cleanly inside standard AR-15 magazine wells. Because the cartridge headspaces on its steep shoulder, proper sizing die setup is critical during handloading to ensure consistent chambering and reliable bolt closure.

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Common Questions

  • Can I form 458 SOCOM brass from 50 Action Express cases?No! While the 458 SOCOM traces its ancestry to the 50 Action Express, the SOCOM case is significantly longer (1 inch and 575 thousandths versus 1 inch and 290 thousandths for the 50 AE), making direct case conversion impossible; factory-formed brass must be used.
  • What is the standard twist rate for 458 SOCOM dimensions?A 1 in 14 twist rate is the most common standard for factory barrels, providing exceptional gyroscopic stability for everything from light supersonic hunting rounds to heavy 600-grain subsonic projectiles!
  • Does the 458 SOCOM require special magazines?While it fits into standard 5-56 millimeter AR-15 magazine bodies, it feeds in a single-stack configuration. Standard followers often work, but specialized or modified followers and magazines improve feeding reliability significantly!

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