As far as I am concerned, the 300Blk is the AR-15 world's answer to the 30 Carbine and like that cartridge is happiest loaded to higher velocities with lighter bullets.
Where have you been looking for load data?
The Hodgdon website (
Hodgdon Reloading | Home) is one source where you will find several supersonic loads for bullets in the 150gr to 180gr weight range. Most of them use the powders that would be familiar to 30 Carbine loaders like IMR-4227 and H-110, but Hodgdon also makes CFE BLK which is specifically adapted to the 300Blk.
Remember that proper reloading procedures are to begin with the Starting load and then work up in increments of 0.3 or 0.4 grain (depending on the difference between starting and maximum) until you get an accurate load that will cycle your gun, you encounter pressure signs or you reach the maximum load.
Good luck.