I'm confused: .223 cal. or 5.56mm?
I have a Colt Match Target HBAR (a post-ban AR-15, essentially: no flash suppressor, no bayonet lug, no collapsible stock).
The rifle's receiver is marked "Cal. 223". (That'd be what I'd call "my first clue," I guess.)
I have always used Remington .223 ammunition, which I bought in a case, for shooting at the range (although I have not had the pleasure of doing that in a long time). The ammuntion I have says .223 cal., but I am confused because it seems to me that people say .223 and 5.56mm interchangeably. But I thought I read a thread on some board that said they are not interchangeable.
Can someone set me straight? Are they essentially the same thing, or are they not, and should I not ever use anything called 5.56mm in my rifle, like for instance if I found a good deal on it?