It's stamped .223 on the back of the upper. Can it safely fire 5.56?
Addressing the ammo issue, .223 Rem, and 5.56mm are virtually the same round, the main difference is, .223 is loaded for sporting purposes, and 5.56mm is loaded to NATO military spec's. The biggest thing you need to concern yourself with is bullet weight. With any Mini-14 it's best to stay with a load that has a bullet weight of 45 to 55 Grs. as they will offer the best accuracy in the Mini-14's barrel twist rate and length. Avoid steel case ammo, it will eventually cause damage to the bolt, shoot brass case ammo only....I have a couple of questions. What are the differences between the .223 & 5.56, I have reloaded military brass in .223s for years & & never had a problem. I'm hearing don't use 5.56 in a .223 chamber.
The next question is has the accuracy of the Mini14 improved? I've known several people who have had them & they weren't very accurate. Has Ruger gotten this sorted out? I like the feel & looks of the Mini14 way above the AR guns.