So, 5.56 NATO and .223 Rem. Two cartridges, identical exterior dimensions, yet the chain of events that occurs once the trigger is pulled makes the two rounds as different as oil and water. Yes, to the naked eye, there is no difference; even to the trained eye, without inspecting the headstamp to verify, I seriously doubt whether anyone could differentiate between the two cartridges unless there was a signature projectile on top. So, what do you need to know regarding 5.56 NATO vs. .223 Rem. to be safe and optimize performance from your rifle? Let’s take a look.