.44 Mag Light loads w/Unique powder
8.8 grains will do just fine..you can use as little as 8.0 grains.
For my light loads I use 8.0 of Promo with a 214 Lee SWC or the Lyman 215 SWC-GC bullet. I shoot a Model 29 and a Ruger Superblackhawk, both with long barrels. I prefer Promo as it is bulkier and a bit more consistent, but there is nothing wrong with using Unique.