I've been messing around, working up some loads for my 673.
61 grs RL-15 ~2678 FPS
62 grs RL-15 ~2733 FPS
59 grs W748 ~2692 FPS (excess pressure signs, bolt sticky to open)
All under a 225 Nosler Part.
The 61 grains of Rl-15 was shooting VERY well, 1" group @ 100 yds.
Quite dissapointed with the W-748. Noticeabley more felt recoil, almost knocked the Chrony over, and less velocity.