5.56 vs .223 vs .223 Wylde: What's Safe to Shoot in Your AR-15
In This Guide
This is the most asked safety question in the AR-15 world — and getting it wrong can damage your rifle or injure you. The short version: .223 Remington and 5.56 NATO look identical, load into the same magazine, and chamber in the same rifles. But they are loaded to different pressures, and shooting 5.56 NATO in a rifle chambered only for .223 Remington can cause dangerously high pressure.
The good news: most modern AR-15s are chambered in either 5.56 NATO or .223 Wylde, both of which safely fire both types of ammo. But you need to verify — not assume.
They Look Identical. They're Not.
A .223 Remington cartridge and a 5.56 NATO cartridge are externally identical. Same case dimensions, same bullet diameter, same overall length. You cannot tell them apart by looking at them in your hand (unless you read the headstamp). The difference is internal: 5.56 NATO is loaded to higher chamber pressure than .223 Remington.
The exact pressure difference depends on which measurement standard you use (SAAMI vs. NATO EPVAT testing methods measure differently), but the practical effect is the same: 5.56 NATO ammunition produces more pressure than .223 Remington ammunition.
The Actual Differences
Chamber geometry (the real issue)
The more important difference isn't the ammo — it's the chamber. A 5.56 NATO chamber has a slightly longer throat (leade) than a .223 Remington chamber. The throat is the unrifled portion of the barrel just ahead of the cartridge.
A longer throat gives the bullet more room before it contacts the rifling. This means a longer throat produces lower peak pressure for the same cartridge. A shorter throat (like a .223 Remington chamber) seats the bullet closer to the rifling, which produces higher peak pressure.
This is why the combination is dangerous in one direction only: firing a 5.56 NATO cartridge (higher-pressure ammo) in a .223 Remington chamber (shorter throat = even higher pressure) compounds the pressure increase. The reverse — firing .223 Remington in a 5.56 NATO chamber — is always safe, because you're putting lower-pressure ammo in a more generous chamber.
Safety Chart: What Goes Where
| Your Chamber | .223 Remington Ammo | 5.56 NATO Ammo |
|---|---|---|
| .223 Remington | ✓ Safe | ✗ NOT recommended — overpressure risk |
| 5.56 NATO | ✓ Safe | ✓ Safe — designed for it |
| .223 Wylde | ✓ Safe | ✓ Safe — designed for both |
Safety Bottom Line
.223 Remington ammo is safe in everything. 5.56 NATO ammo is safe in 5.56 NATO and .223 Wylde chambers. 5.56 NATO ammo should NOT be fired in .223 Remington-only chambers. When in doubt, check your barrel markings or manufacturer specs.
.223 Wylde: The Best of Both
.223 Wylde is a chamber specification (not a cartridge) designed by competitive shooters to safely fire both .223 Remington and 5.56 NATO ammunition while optimizing accuracy. It uses a throat geometry that's a compromise between the .223 Remington and 5.56 NATO specs — long enough for safe 5.56 pressures, tight enough for excellent .223 accuracy.
If you're building an AR-15 or buying a new barrel, .223 Wylde is the best choice. It gives you complete ammo flexibility with no safety concerns and a slight accuracy edge over a standard 5.56 NATO chamber. Many premium AR-15 manufacturers (including Aero Precision, Ballistic Advantage, and Faxon) offer .223 Wylde as their default or premium barrel option.
How to Check Your Chamber
Your barrel should have the chamber specification stamped or engraved on it. On an AR-15, look on the barrel near the muzzle device or near the barrel extension (where it meets the upper receiver). Common markings include "5.56 NATO," ".223 REM," ".223 WYLDE," "5.56x45," or ".223."
If you can't find a marking, check the manufacturer's website or contact them directly. Do not guess. Most modern AR-15s from major manufacturers (Smith & Wesson M&P15, Ruger AR-556, Springfield SAINT, SIG M400, PSA AR-15s) are chambered in 5.56 NATO, which safely shoots both. But some precision or varmint-specific AR-15s may be chambered in .223 Remington only.
What Ammo to Buy for Your AR-15
If your barrel says 5.56 NATO or .223 Wylde (the vast majority of AR-15s): buy whatever's cheapest. Both .223 Remington and 5.56 NATO are safe. Look for bulk 5.56 or .223 at the best cost per round.
If your barrel says .223 Remington only: stick to .223 Remington commercial ammo. You'll have plenty of options — virtually every ammo manufacturer makes .223 Remington loads.
For home defense: 5.56 NATO 55gr or 62gr is the standard recommendation. Lighter, faster 5.56 rounds tend to fragment in drywall, which can actually reduce overpenetration risk compared to handgun rounds — a counterintuitive fact we cover in our home defense ammo guide.
For range practice: The cheapest brass-cased .223 or 5.56 you can find. Currently that's running approximately $0.25–0.44/round depending on whether you buy steel-case or brass. Check our 5.56/.223 deals page for current pricing.