Norma 203B
I don't know what it is, but this powder produces the most accurate load, consistently, ever shot out of all my AR's.  Its simply the KING load.  25.1 grains of 203B using 2.255 OAL Sierra Match King 69 grains, is just incredible.  (its the lower left load, and right next to it at .34 is 25.3 grains.