Take it up with Rummychick, I responded to a single post.
Either way, your post was bunk.
It ain’t the ammo, it’s the gun. I know I’m a little late to the discussion, but any decent AR platform is designed for 5.56 ammo and will shoot .223 no problem. The issue is with guns designed for .223, like a bolt action varmint rifle, can’t handle the pressures of a 5.56. A .223 or 5.56 will feed just fine in either gun. The bullet (say a 55 gr.) is identical, the casing of a 5.56 is a little heavier and are loaded a little hotter.
And that was your mistake. You made a fool of yourself doing so.