One I have looked at is stamped, ".223". I understand that the Mini-14 TARGET rifle is chambered for .223 ammo ONLY. Question is: Is this #580-6XXXXX rifle chambered for .223 or 5.56 NATO? (For the uninitiated, the 5.56 NATO uses the same case as .223 Remington, but has a longer throat. Firing the NATO ammo in a rifle chambered specifically for the civilian round could produce higher pressures!