Quote Originally Posted by TH76251556 View Post
The AR was built and designed to shoot the .223/5.56 cartdrige.
It was initially designed for 5.56x45, but with the advances in technology since its initial design it will shoot a number of other cartridges reliably. Same holds for 7.62x39 and the AK. You can now literally choose your platform independently of the cartridge you choose.