The 300 AAC was designed for suppressed AR's. If you are running suppressed then you need to be running subsonic. Why try and push a .308 down to subsonic is you don't need to. Also .308 is an AR-10 platform and one of the issues with AR-10 is that unlike AR15 there is no standard. Some guns are CMMG, some are Armalite and some (like the Matrix Aerospace that I built) are a combination. THe AR15 will let you switch between MANY calibers by swapping uppers.