5.56x45 NATO vs .223 Rem

I always go by what I was instructed by way back when I was in the Army Reserve.  .223 Remington ONLY in .223 Remington chambered firearms.

5.56 or .223 in firearms chambered for 5.56

And I have shot a lot of .223 out of my Franken-15.  And one thing I have noticed, the steel cased .223 has much less recoil impulse and is much dirtier than any 5.56 I've fired, steel or brass cased.