Totally ok for shooting out of a rifle chambered in either .223 Rem or 5.56, the .223 frangible is specifically designed to fall apart on impact with a hard service. These are excellent for close-range steel targets, shoot-houses and CQB training. The projectile is made of compressed metals, making them more fragile than an FMJ.
Note that despite their more fragile projectile, these are extremely lethal.
Brass: New or Reman
*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