There's a good article at military.com about this weapon. It's already been rejected. Google it and you'll find several other articles saying at's a good weapon, but didn't perform to military standards.

As for the .243 overheating barrels, I'm not sure that would happen. With the types of barrels out there now, it's not such an issue. Look at the new M60E4. It can fire 800 rounds straight without stopping and no overheating. Only the Navy is using the M60 now, but this type of new barrel is being looked at as being the standard for any new rifles developed.