[RummyChick]

They aren’t interchangeable if your gun has only a .223 chamber.

If it is chambered for both then it can handle both.

I have read enough on this in the few minutes to see that if it is only chambered for .223 it can cause a problem.

THEY ARE DIFFERENT CASINGS.

And it is relevant if Vance said they were .223 casings.

[RummyChick]

http://www.humanevents.com/2011/02/15/223-remington-vs-556-nato-what-you-dont-know-could-hurt-you/

“ATK, the parent company of ammunition manufacturers Federal Cartridge Company and Speer, published a bulletin entitled “The Difference Between 223 Rem and 5.56 Military Cartridges.” In this bulletin, ATK stated using 5.56 ammo in a .223 rifle could result in “…primer pocket gas leaks, blown cartridge case heads, and gun functioning issues.” “

[Uncle Chip]

And it is relevant if Vance said they were .223 casings.

Where has he said anything about casings yet???

[bluecat6]

Physical risk of shooting 556 from 223 only rifle....different pressures due to different projectile.

Firing a 556 from a 223 only is putting the shooter in danger.