I have used it with 140 gr bullets, using H4350 load data. After a fair bit of work, I found in my gun, best accuracy was with H4350, a full load of H1000 was second in accuracy with about the same MV as H4350, and highest MV was with a full load of RL25 (I just wish it was more accurate).
RL17 did not warrant further work. It's a suitable powder for the 6.5X55 for 140 gr and lighter bullets and might work well in your gun - worth a try at least.