.223 Remington vs 5.56 NATO
Last reviewed · 1 source
Short answer: .223 Remington is a commercial cartridge with an industry standard published by SAAMI. 5.56×45mm NATO is a military cartridge, and it does not appear in SAAMI’s centerfire rifle standard. [SAAMI Z299.4-2025] Whether a given rifle can safely fire one or both depends on its chamber. Follow the marking on the barrel and the manufacturer’s instructions.
What the .223 Remington standard specifies
SAAMI Z299.4-2025 (Centerfire Rifle) lists 223 Remington [223 REM]. Its cartridge and chamber drawing was issued 04/21/1980 and last revised 09/25/2023. [SAAMI Z299.4-2025]
| SAAMI item (223 REM) | Published value |
|---|---|
| Maximum Average Pressure (transducer) | 55,000 psi |
| Maximum Average Pressure (copper crusher) | 52,000 CUP |
| Velocity & pressure test barrel length | 24.000 in |
| Test barrel twist | 1 turn in 12.00 in, right-hand |
| Test barrel bore / groove diameter | .219 in / .224 in |
SAAMI defines Maximum Average Pressure as “the recommended maximum pressure level for loading commercial sporting ammunition.” [SAAMI Z299.4-2025]
How 5.56 NATO differs
Read your barrel marking
What is .223 Wylde?
Buying ammo
Check your chamber marking first, then compare price per round including shipping. Prices on the same load can vary widely between retailers.
Related
Sources
- ANSI/SAAMI Z299.4-2025 — Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Ammunition. Sporting Arms and Ammunition Manufacturers' Institute (SAAMI). [industry] Accessed October 26, 2026. Reviewed from SAAMI's published PDF. TODO: replace url with the direct standards-page link once confirmed reachable.