Using commercial .223 cartridges in a 5.56-chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223-chambered gun due to the excessive leade. There always seems to be a lot of confusion over the difference between a .223 and a 5.56 chamber. I often receive questions asking if someone can shove 5.56 ammo into their new AR-15. The quick answer is maybe. Just because a gun has .223/5.56 scribed on the barrel, does not mean it can handle either piece of ammunition equally.