Short answer: 5.56 NATO and .223 Remington look almost identical, but they are loaded differently and chambers differ. Check the barrel marking before you shoot.
The key difference
5.56 NATO ammo is usually loaded to higher pressure than .223 Remington. The chamber of a barrel marked 5.56 NATO is made to handle it. A barrel marked .223 Remington may have a tighter chamber.
What your barrel marking means
- 5.56 NATO: designed for 5.56 and .223 ammo.
- .223 Wylde: designed to handle both well.
- .223 Remington: use .223 ammo.
Choosing ammo
Match the bullet weight to what you are doing. Lighter bullets are common for plinking and practice. Heavier bullets are common for longer range. Our .223 / 5.56 ammo guide and ammunition by caliber guide help you pick.
Building a 5.56 rifle
See the 5.56 NATO AR build guide for parts that go with this caliber.
Where to go next
Browse AR-15 parts, read the custom AR-15 build guide, or have our shop in Palmetto, FL help with gunsmithing and custom AR builds.
Which Ammo Is Right for Your Rifle
The difference comes down to pressure and chamber shape. 5.56 NATO is loaded to a higher pressure and is built for a slightly longer throat, while .223 Remington is loaded to a lower pressure. A barrel marked 5.56 NATO, or a .223 Wylde chamber, handles both. A barrel marked .223 Remington is meant for .223 loads, so check the marking on your barrel before you buy a case.
Cost and Accuracy
Steel-case and M193 style 5.56 is usually the budget choice for practice. Match grade .223 and heavier 77 grain loads tend to group tighter, which matters for long range or precision builds. If you shoot a lot, keep a cheap practice load and a better load for accuracy work.
Barrel Twist Matters Too
A 1:7 twist stabilizes heavier bullets, while 1:9 suits lighter 55 grain loads. Match your ammo weight to your twist rate for the best groups.
Browse our in-stock ammunition, or call the shop and we will help you pick a load for your barrel.