IME, powders run toward the high end of their load range burn cleaner than at the low end ...... smokeless powder burns progerssively, the higher the pressure, the faster (and more completely) they burn ....
That said, the cleanest burning powder I've ever used was Vihtavouri vN340 ..... loaded at top levels with jacketed bullets in .45 ACP, I could run through a couple hundred rounds and the gun was almost not dirty enough to bother cleaning ....... running the old Red Dot at 5 grains with a plated bullet ..... you'd need to wipe your hands after 100 rounds .....
