I don't load .45 ACP yet, but in my .38 special, .357 magnum, and .45 colt loads I use Clays powder by Hodgdon. It burns very clean and is not position sensitive (some powders are position sensitive, especially with the lighter loads that we cowboy action shooters use). It's also very consistent when you check your loads with a chrono. I also use Clays in my shotgun loads. Come to think of it, Clays is the only smokeless powder I'll use anymore. I load a lot of black powder loads, but that's a whole other story.