.223 fires completely fine through a rifle chambered in 556.
Its the other way around that you would be worried about firing 556 through a rifle chambered for .223.
Thank goodness your smith was there to save the day though.
He will probably test fire your rifle with it when he goes to test it out haha ...sorry its just funny to me.
What he was saying is that the .223 ammunition did not have enough "oomph" to cycle the bolt. He is NOT going to be test firing the rifle.
One of the things that annoys me about factory ammo is that it is about impossible to tell what kind of pressures it really develops, etc. So who really knows. It just seems a little strange to me.
I was already aware that firing 5.56 thru a .223 was a very bad idea.