The 5.56mm NATO is loaded to higher maximum pressures than the .223 Remington.
| Cartridge | Velocity (40gr) | Barrel Life | Availability | | :--- | :--- | :--- | :--- | | | 4,150 fps | 1,500 rounds | Wildcat (custom) | | .220 Swift | 4,100 fps | 1,800 rounds | Commercial | | .22-250 Rem | 4,000 fps | 2,000 rounds | Commercial | | .204 Ruger | 3,900 fps (32gr) | 2,500 rounds | Commercial | | .224 Valkyrie | 3,050 fps (90gr) | 3,000+ rounds | Commercial | 223 mkv