Most AR-15 rifles are chambered in 5.56 or .223. What’s the difference between the two rounds, anyhow? They’re supposed to be interchangeable…kinda, sorta, maybe…aren’t they?
The difference is in the round itself: the NATO round is a little bit hotter. The case is the same size, but the powder charge, projectile and also the rifle specifications differ slightly. That means 5.56 rounds produce more pressure in the chamber than .223 Remington rounds. As a result, you want to make sure to check your AR-15 to see which it’s chambered for, as not all AR-15 rifles sold to civilians are the same.