To further clarify things for RustyPelican,
The .223 Remington and the 5.56 NATO cartridges are extremely simliar cartridges but not quite the same. This does not GENERALLY prohibit one cartridge being used in the other chamber.
Essentially, without getting into 50 years of history and making things really confusing, the .223 Remington was the direct, developmental predecessor for the cartridge that became the 5.56 NATO cartridge.
As the adoption process went along its' merry way, the dimensions for brass and chambers were finalized to specs that are just a wee beit different. Essentially the NATO cartridge is a wee bit "beefier" dimensionally. In your average autoloading rifle the difference is negligable.
Now, when you get to bolt guns or rifles with Match chambers....then it becomes more important to know which cartridge you truly need to be using. Using 5.56 NATO in a .223 Remington rifle with a tight or Match chamber can be courting high pressures and very difficult extraction. This is because the dimensional profile of the 5.56 NATO is slightly large in certain areas, mostly concerned with the case neck and should dimensions.
As far as your Match Target, it is listed as .223 on the reciever but the actual barrel is chambered to the 5.56 NATO dimensions. Since the dimensions of the civilian counterpart, the .223 technically fall INSIDE the dimensions of the 5.56 NATO, you can use either cartridge interchangeably.
So...in short....go shooting and go have some fun.