I just bought 6lbs of a surplus Unique and have no intention of changing anytime soon! It is the BEST powder for the 45Colt, bar none. Dirty? Sure! It is a law of thermodynamics, make a fire, there is soot. (Skip paraphrased!) Add lead bullets and the lube, more dirt.
Here is my M25 -7 after 200 rounds or so of a pure wheel weight cast 45-270SAA Penta Pin hollow point, around 260gr as cast, 9.0gr of Unique or this surplus powder. Dirty? Yep! Still, all of the bullets went right were I wanted them to go! That is something that you cannot overlook!
Then, after wiping it off with a soft dry towel, here is what it looked like. Let me ask you this: Aren't you going to clean your guns after you are done shooting anyway?
Take a look:
So, how big of a deal is this "dirty" thing anyway?
Not that big of a deal for me.
Now, as for Unique liking it hot. It most assuredly does, oh, and by the way, so do 99.999999999999999999999999999% of most other powders. 2400 is no different. It likes it at the top of its data too. That is why you have one powder for uber light rounds, another for midrange and yet another for WILD!
That is what makes life as interesting as it is. Experiment around some!
It is a blast: Pun intended!