Not sure if you saw this:

http://www.thefirearmblog.com/blog/2...ac-blk-rifles/

Savage claims that they could not get the accuracy they wanted from 300BLK subsonics so they scrapped their project to bring out a 300BLK rifle. They hinted that they could get good accuracy from the 300BLK supersonic loads, but not the subs.

Take it for what it is worth, if you are going to shoot supersonic that could be a cool project. But for me, I'd rather shoot a 308 if I'm planning to shoot 30cal over the speed of sound.