Quote Originally Posted by thamm View Post
Barrel and muzzle device are the only parts different between a .223 upper and a .300 AAC upper. The receiver, BCG, gas system, etc are all the same.
Well duh, BUT....by the time you spend the money to buy the tools to change the barrel yourself you might as well just buy a complete upper and eliminate the hassle of having to swap barrels back and forth on the same upper. Given how cheap .300 AAC upper assemblies are right now (starting around $250) it's pretty much a no-brainer.