I've used HP-38/231 and 700X for cast in 32 S&W, 44 Mag, and 45 Colt. In the end I always end up going back to Unique or Trail Boss for cast loads.
I've never gotten very good accuracy with HP-38/231 in anything I've tried it in. I still have most of a pound I bought probably 15 years ago on the shelf because it never ends up getting used beyond test loads with new guns. I was actually just fiddling with it in a new Cimarron 1873 rifle in 45 Colt about a week ago. Several groups of it didn't even keep all the shots on paper at 50 yards.
700x has shot good groups with midrange charges in my 32 and 44, but just terrible in 45 Colt. For some reason I tend to get real bad fliers with it, though, even when I have a great core group.
Blackhorn 209 has produced some fantastic groups in 327 Fed, 44 Mag, and 45 Colt for me, but it's too expensive to really be viable compared to standard powders. You also gotta love cleaning guns if you're gonna use it. It cleans up easy, but it's a filthy shooting powder and it stains brass pretty badly.
