[Lazamataz]

Like the others say, get an AR-15 in .223/5.56 NATO (they are virtually the same cartridge and ar inter changeable)

DUDE! They are NOT interchangeable!

It is safe to fire a .223 round from most 5.56 mm firearms, but it is not safe to fire 5.56 mm rounds from a .223 firearm. Because these two rounds look very similar and have the same size case, always check the head stamping on your ammunition before loading your firearm just to be safe.

[tumblindice]

Precisely Laz. The 5.56 has a longer leade. The leade is the part of the barrel immediately in front of the chamber where the bullet travels before engaging the rifling.
Bad things can happen if you try to fire 5.56 through a .223 barrel.
The type of barrel you have should be roll stamped on the barrel.
Fire .223 through a 5.56 barrel all you want.