Dennis, this is only capable of firing .300 Blackout. Where it says 5.56 magazine, they are sending you a standard AR15 magazine, which can also hold .300 Blackout cartridges.
Stay safe & have a great day!

No, this will Only shoot what it is chambered for which is the .300 Blackout. The mags included are standard 5.56 which also can hold .300 Blackout rounds.

Hi Dennis and welcome. This rifle can only shoot the caliber 300 Blackout for which it is chambered. The shell case for the 300 blk is derived from the 5.56/223 so the same magazine works for both. Cheers and stay safe!