Finally, this is the answer to my 30 caliber prayers for the AR15. The 300 AAC blackout. It seems that all you have to change is the barrel. Everything else, including the bolt carrier, handguards, buffer, upper, lower, and even the magazines (including the followers) stays the same as the 5.56 version! I will be watching this one to see if the price goes down and to see the longevity of the rifles with this.