.223 and 5.56 are Interchangeable, Right?

Doug Howlett

Not exactly. The .223 and 5.56 NATO may look identical, and they are very close to being the same size, but there is a difference. Yes, you can safely fire .223 Rem. in an AR chambered for 5.56, though gun writer Richard Mann at Field & Stream notes “in some cases, precision can be less than stellar.”

So, what about the reverse? Not a good idea the experts say. The key difference? Pressure. The 5.56 operates at a higher pressure—up to 61,000 psi compared to the .223 Rem.’s 55,000 psi—and that extra punch can create serious safety risks if fired in a .223 chamber. The reason? The .223 chamber has a shorter throat, making even higher pressure spikes possible, which can result in damage to the firearm—or worse, you.

Check your barrel markings—they’ll tell you whether your rifle is chambered for .223, 5.56 or both. Or get a rifle chambered for .223 Wylde—a hybrid chamber that allows for safe and accurate use of both cartridges. Bottom line? Stick to what your rifle is built for, and if in doubt, consult your manufacturer before stockpiling ammo or pulling the trigger.