Can I shoot .223 in a 5.56 rifle?

Yes. A 5.56 NATO chamber safely fires .223 Remington ammunition. Accuracy can be a little lower than in a .223 chamber, but it's safe.

Can I shoot 5.56 in a .223 rifle?

It isn't recommended. 5.56 NATO loads run at higher pressure and the .223 chamber has a shorter throat, so pressure can exceed what the rifle was built for. SAAMI lists it as an unsafe combination.

A chamber design that fits between .223 and 5.56 dimensions. It safely fires both rounds and is common on accuracy-focused AR-15 barrels.

.223 Remington vs 5.56 NATO: Are They the Same?

The short answer

The two rounds look identical, but 5.56 NATO runs at higher pressure and is meant for a chamber with a longer throat. A rifle marked 5.56 NATO or .223 Wylde can fire both. A rifle marked .223 Remington only should fire .223 Remington only.

What's different

The cases have the same outside dimensions, so either round fits in either chamber. The difference is inside the rifle: a 5.56 NATO chamber has a longer leade (the space before the bullet meets the rifling), and 5.56 loads are made to run at higher pressure.

Fire a 5.56 round in a tight .223 chamber and pressure can climb beyond what the rifle was designed for. SAAMI, the US ammunition standards body, lists that combination as unsafe.

Check your barrel

Marked 5.56 NATO or 5.56x45: fires 5.56 NATO and .223 Remington.
Marked .223 Wylde: a hybrid chamber that fires both.
Marked .223 Remington or .223 Rem: fire .223 Remington only.

The marking is usually on the barrel near the muzzle or under the handguard. When in doubt, ask the maker.

Which to buy

For most AR-15s, both work, so buy on price and purpose. Brass-cased 55 grain FMJ is the usual range load in both. Heavier 62 to 77 grain bullets suit faster rifling twists (1:7 or 1:8) and longer shots; lighter varmint bullets suit 1:12 and 1:9 barrels.

Compare current prices on the .223 Remington and 5.56 NATO pages. Both open sorted by price per round.

Common questions

Can I shoot .223 in a 5.56 rifle?: Yes. A 5.56 NATO chamber safely fires .223 Remington ammunition. Accuracy can be a little lower than in a .223 chamber, but it's safe.
Can I shoot 5.56 in a .223 rifle?: It isn't recommended. 5.56 NATO loads run at higher pressure and the .223 chamber has a shorter throat, so pressure can exceed what the rifle was built for. SAAMI lists it as an unsafe combination.
What is .223 Wylde?: A chamber design that fits between .223 and 5.56 dimensions. It safely fires both rounds and is common on accuracy-focused AR-15 barrels.

General information, not professional or legal advice. Always follow your firearm maker's ammunition guidance and your local laws.