This is right from the IMR page: This large grained flake powder is at its best when used in heavy field loads from 10 gauge to 28 gauge. In handgun cartridges, 800-X performs superbly in cartridges like the 10mm Auto, 357 Magnum and 44 Remington Magnum. Excellent velocity and uniformity translate into top accuracy.
I got my loading info. from my Hornady Manual it has loads for the .38 spl using 800x, i thought that was kinda odd because i cant find data from IMR for the .38spl. but i loaded some up and they shoot well,thats why i dont totally trust my Manual,i try to get a feel of what other people are using.