[E. Pluribus Unum]

Look on the lower and barrel and see if it is rated for. 223 only or 5.56. Shooting the former in the latter can cause problems. (The reverse is fine though.)

You have it exactly reversed.

5.56 has higher pressure than .223.

You can safely fire .223 in 5.56, but not the opposite.

That being said, lots of people do it anyway.

.223 Wylde will fire both. The throat length is a compromise between the two.

[mnehring]

You are right. Bad wording. You shouldn’t fire a 5.56 in a. 223 rated firearm.

[Dead Corpse]

The chamber dimensions on the .223 are different from the 5.56. It’s the leade, the distance from the projectile to the first set of rifling, that is different. The difference in this gap can cause a dangerous over-pressure condition in the .223 chamber when shooting 5.56 spec’ed rounds.

So while it IS a pressure problem, it isn’t the powder charge in the case that is causing it. Just want everyone to be clear about that as it has spawned a billion and one odd “gun counter” rumors.

Also depends on platform. Pencil barrels with a thin chamber wouldn’t survive. A stainless bull barrel probably wouldn’t notice. Your mileage may vary...

[snoringbear]

“You can safely fire .223 in 5.56, but not the opposite.”

Yes and no. Example, I own a Ruger Mini 14 Ranch. At the Ruger website in the FAQ’s the question is asked “is it ok to shoot 5.56mm in my Ruger .223?” Ans; yes, with the exception of the Ruger Mini 14 Target Model. So, it’s best to check with the manufacturer of your .223 before shooting 5.56mm. Just saying :)