The same powders that work well in the longer barrels will do in the shorter ones. I use R19 in my M700 and Kimber M84 with 140gr bullets. H4831 is also a good powder to try.
I asked the same question about two months ago. NOSLER says the rifle data is very valid to use in the 15" Encore. I also have an A-Bolt SS, and love it. It is the single most accurate totally factory gun I own. I love the caliber too!
