The short answer
You can safely shoot .223 Remington in a rifle chambered for 5.56 NATO. You should not shoot 5.56 NATO in a rifle chambered only for .223 Remington. The cartridges are dimensionally nearly identical, but 5.56 NATO is loaded to higher chamber pressures.
If your barrel or receiver is stamped "5.56 NATO," "5.56x45," or ".223 Wylde" — you can shoot both.
If your barrel is stamped only ".223 Rem" or ".223 Remington" — stick with .223 Remington ammo.
Why they're different
The two cartridges were developed in parallel — .223 Remington as a commercial sporting round and 5.56 NATO as a military specification — and share the same external dimensions. A round of .223 and a round of 5.56 look identical and load into the same magazine.
The differences are internal:
Chamber dimensions. The 5.56 NATO chamber has a slightly longer throat (the leade — the unrifled portion ahead of the cartridge). This extra space reduces peak chamber pressure. The .223 Remington chamber has a shorter throat, which means a 5.56 NATO round (loaded to higher pressure) in a .223 chamber can spike to unsafe pressures.
Pressure specification. Both cartridges operate at roughly 55,000 psi MAP, but NATO and SAAMI use different measurement methods (copper crusher vs piezoelectric transducer) and reference different test points, making direct comparison imperfect. The practical result is that 5.56 military loads tend to run hotter than commercial .223 — not dramatically, but enough to matter in a tight .223 chamber.
What about .223 Wylde?
.223 Wylde is a hybrid chamber designed to safely fire both .223 Remington and 5.56 NATO while maintaining the tighter tolerances of a .223 chamber for improved accuracy. It's the best of both worlds and has become the standard chamber for most quality AR-15s.
If you're buying a new AR-15, look for .223 Wylde chambering. You get full 5.56 compatibility with match-grade accuracy.
What to buy
For a 5.56 NATO or .223 Wylde rifle, buy whichever is cheaper — you can shoot both. In practice, this usually means buying the cheapest brass-cased FMJ available regardless of whether it's headstamped .223 or 5.56.
For a .223-only rifle (typically bolt-action sporting rifles, some older ARs, and some Mini-14 variants), buy .223 Remington ammo. It's widely available and often priced identically to 5.56.
Compare .223 prices → | Compare 5.56 prices →
Price difference
Minimal. Both calibers track closely in price since they use the same components. Military surplus 5.56 (like Federal XM193 or PMC X-TAC) is sometimes slightly cheaper due to high production volume. Premium .223 match ammo (like Hornady Match 73gr ELD or Black Hills 77gr) runs more because it's precision-loaded.
Check the Ammo Price Index for current CPR →
Common misconceptions
"5.56 is more powerful than .223." Marginally. The velocity difference is typically 50–100 fps for the same bullet weight, which translates to a small increase in energy. For practical purposes, they perform identically on target.
".223 is more accurate than 5.56." Sometimes. .223 Remington match ammunition is loaded to tighter tolerances with better bullets. But this is a function of the ammo quality, not the cartridge specification. Military-spec 5.56 prioritizes reliability over accuracy. Buy match-grade in either headstamp for accuracy.
"I can just shoot 5.56 in my .223 — it's fine." It usually is, but "usually" isn't a standard you should apply to chamber pressure. If your rifle is chambered .223 only, the manufacturer designed it around .223 pressure specs. Exceeding those specs — even if nothing goes wrong 99% of the time — puts stress on the action that it wasn't designed for.
The bottom line
Check your barrel stamping. If it says 5.56, .223 Wylde, or 5.56x45 — buy whatever is cheapest. If it says .223 Remington only — buy .223 Remington. It's a simple rule that eliminates any safety concern.
Search for the best price on .223/5.56 →
Related articles
Related caliber pages
- 5.56 NATO ammo prices — Current pricing across all retailers
- Cheapest 5.56 NATO right now — Lowest observed prices
- 5.56 NATO price history — 30-day pricing trends
- .223 Remington ammo prices — Current pricing across all retailers
- Cheapest .223 Remington right now — Lowest observed prices
- .223 Remington price history — 30-day pricing trends
Sources
- SAAMI .223 Remington Specifications — Official chamber pressure standards
- 5.56×45mm NATO — Wikipedia — Cartridge history and military adoption
- .223 Wylde — Wikipedia — Hybrid chamber design