Totally ok for shooting out of a rifle chambered in either .223 Rem or 5.56, the 223 options listed here are designed for more than just close-range plinking. Each bullet profile has a specific purpose as indicated below.
Brass: Some of our Special Purpose .223 is loaded only in new brass. For precision shooting, we feel it's essential that each piece of brass is identical so the load is precisely the same between each round.
*IMPORTANT: Though both cartridges look identical, 5.56 is loaded to a higher pressure than .223, which is why rifles chambered for a 5.56 cartridge can fire .223, but it is not recommended that 5.56 cartridges are fired out of a rifle chambered for .223