Me neither without RS60, perhaps someone else will chime in.
Average for 6.5 CM should be 2500-3000 but if you’ve been pumping them out at 3000 FPS with N550 then that could be it, i bet you’ve got some throat erosion ?
I’ve heard good things about the 147 but you have to put them down at 2700+ to get optimal stability from a 1:8 twist, 1:7 seems to be a popular option for this particular bullet.