IMR 3031
Here is IMR3031 next to a couple other powders in its burn rate "area".  H322 is faster burning, and Shooters World Tactical Rifle is slower.  But as you can see, all 3 of these powders are better suited for lighter 5.56 bullets.

IMR 3031 is a stick powder, with very large sticks.  Its very dark, black even.  A very old powder, but as you can see, its comparable in performance using similar bullets, shot same day, same conditions.  That being said, I think H322 is superior, as its temp stable and slightly more accurate, I would estimate. 

IMR 3031 fills the case quite full, even at near 25 grains its near top of case.  Due to this, you can't go super high velocity using this in 50-64 grain bullets, because you would have to massively compress the load.  These are ALL already compressed.  And look at the velocity!  This is 20" Barrel.  Shilen 1:7.5 twist.  Its basically near 150 FPS less velocity using similar charge as H322. 

Of note, bottom 2 (Left and middle) are using Sierra GAME CHANGER 64 grain bullets, but button right is using 62 grain M855 steel core.    Also please note, Shooters World Tac Rifle is using different bullets.