Can you shoot 5.56 in a .223 chamber?
Not safely. The .223 chamber has a shorter throat, so 5.56 pressure climbs past what the rifle was proved for. The reverse direction is fine.
The two cartridges are dimensionally close enough to chamber in each other, so this comes down to pressure rather than fit. The difference is the leade — the short unrifled section ahead of the chamber before the bullet meets the rifling.
A 5.56 NATO chamber has a noticeably longer leade than a .223 Remington chamber. Put 5.56 ammunition, which is loaded hotter to begin with, into the shorter .223 throat, and the bullet engages the rifling sooner. Pressure rises above what a .223-chambered rifle was proof-tested for. What that produces ranges from hard extraction and accelerated wear to, at the far end, a failure.
| .223 Rem in a .223 chamber | Correct |
|---|---|
| .223 Rem in a 5.56 chamber | Safe — the usual advice |
| 5.56 NATO in a 5.56 chamber | Correct |
| 5.56 NATO in a .223 chamber | Not recommended — overpressure |
| Difference | Leade length ahead of the chamber |
| Middle ground | .223 Wylde, cut to take both |
If you want one rifle that digests both without the argument, that is what a .223 Wylde chamber is for — it uses the longer 5.56 leade with tighter dimensions elsewhere. Read the barrel marking rather than the receiver: a rifle marked .223 Wylde or 5.56 NATO will take both, and one marked .223 Rem should be fed .223.
Caution: Chambering is not the test here. A 5.56 round will load and fire in a .223 chamber without protest, which is why this is a marking question rather than something you can feel.
Sources
- NRA Shooting Sports USA — understanding semi-automatic chambers
- 5.56×45mm NATO — chamber and pressure specifications
- .223 Remington — SAAMI standardisation
Last checked 2026-09-02. Specifications change between production runs — verify anything safety-critical against your own firearm and the manufacturer before acting on it.
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