More data from the Mar 25th 2019 session with different bullets:
Savage 12 FV 6.5 mm Creedmoor 5 round Groups Sightron 36x42mm
# Grps Load Description Bullet Weight Velocity Average Median St Dev 1 2 3 4
4 IMR4350 41.8 gr 2.815 130 Hornady ELD-M 2719 1.910 CCI BR-4 wf 1.361 * Lapua SRP 49/47 deg F. Hornady Match # 26177 130 2719 0.362 0.369 0.095 0.240 0.351 0.387 0.468
3 IMR4350 41.3 gr 2/820 147 Hornady ELD-M 2659 1.910 CCI BR-4 wf 1.361 * Lapua SRP 47/44 deg F. Hornady Match # 26333 147 2659 0.337 0.301 0.074 0.287 0.301 0.422

Today's average was 0.351 for 7 groups.
Mar 20th average was 0.398 for 8 groups.
Overall average for all groups (all bullet weights) is now 0.376 for 15 groups.

It appears that this rifle likes the heavier bullets, just like I had hoped.
My other 6.5mm CM 26-inch barrel 12 LRP also likes heavier bullets so this 12 FV can be the load development mule for the more expensive 12 LRP and take some of the work off its barrel.

Weight Average Median St Dev
130 0.399 0.403 0.099
140 0.406 0.406 0.055
142 0.358 0.359 0.040
147 0.337 0.301 0.074