The .458 SOCOM is a moderately large round designed for the AR-15 Platform. The cartridge was made to be 100% compatible with many of the AR-15 parts. The .458 SOCOM round fits in .223/5.56 magazines but single stacks rather than double stacks.
Anderson Manufacturing AR-15 .458 SOCOM Bolt Carrier Group
Anderson .458 SOCOM Bolt Carrier Group - Phosphate