I have a 6.5" 25-5 and shot some loads of 8 grains of Unique under a 255 just about two hours ago. Unique is a good powder for the 45 Colt, better than most for sure. Unique is the standard by which all other loads are measured in 45 Colt and for good reason. I have shot Universal extensively in it and was NOT getting the consistency I was looking for until I was well into the +P range and recoil was beginning to be noticeable. This is the ONLY cartridge I load that Universal has not worked better than Unique in though......
I have tried Clays with listed loads and found them to be somewhat more position sensitive than I wanted, same for Blue Dot and Super Field. The more I think about it the more I want to try Power Pistol in it, it should be tops but I have not tried it yet. The softest loads will be the slowest powder. H110/W296 is not very friendly, but 2400 should be good in midrange loads. 4227 should also be quite soft shooting.
You need to get away from the 250 grain bullets. Shoot some 200's and the recoil drops DRASTICALLY. No way I would hand a newbie my 25-5 with a 250 doing 850fps, not even at 750. To you and I it is a big ol' kitty cat, but to a newbie it packs a wallop. Most of my shooting buddies even avoid the 45 Colt with 250+ grain bullets.
The 45 Colt is just not practical to load light with the MASSIVE capacity it has. You need very bulky powders that are position insensitive and burn well at garden hose type pressures, and that is hard to do. Unique is what I would try for the newbies, loaded under 200 grain bullets.