IMO Unique is considered the powder for the 45 Colt because Unique has been around almost as long as the 45 Colt and originally there really wasn't another choice. When your great grandfather, grandfather and father all used Unique for the .45 Colt so will you and not even think of using anything else. I on the other hand like to try new powders in old favorite and sometimes I find a gem.
I'm weird, I guess. For years and years I steered away from Unique. I started with Bullseye and Blue Dot, migrating to H110 & AA#9. Everyone that I knew said the same things about Unique even though they used it over and over and over and .....you get it, while shooting competition.
I reloaded for quite a while before I bought my first pound of it. When did I? When I got my first 45 Colt! I thought to myself as Rule says, if it was good enough for greatgrandpa (I have no idea if he ever reloaded one round), it was good enough for me!
All kidding aside, there is just something so American, so Western, so nostalgic about the Ole' Colt cartridge that begs to be loaded with its old nemesis, Unique! Like peanut butter and jelly, like biscuits and gravy, like baseball & hot dogs and apple pie! I mean, they just go together!
So much so, I got tired of buying Unique one pound at a time but wanted to get it even cheaper. So, this past month, I went and bought 6lbs for $60 from gibrass.com.
Does it meter poorly? Yep, but you can get around it. #1: Don't try to use it in less than a 5gr charge. #2: Put a weight on the top of the powder. I load on Dillon presses and have a low powder sensor. What I do is place a tool head on top or a die or something, to help it stay pressed down into the feed portion and I get +/- .1gr charges. Pretty good for this old warhorse!
The other thing, dirt. Yes, it is dirty. It will make your gun dirty, no two ways about it. It will get all over you too and you will have to wash. Get over it!
Here are some pictures of my M25 -7 after about 300 rounds of 45-270SAA HP boolits and 9.0gr of Unique. Then, there are pictures after a soft rag was used to wipe it down.
Pretty simple and it works great. If you want it to run cleaner, use it at the upper end of its loading data.
Hope this helps!