Loading a 6.5 creedmore and 7 mag. If only used one powder for both, what would you choose? Medium to heavy for caliber bullets.

N550 or RL-19

IMR 4350

I'd try either IMR4350 or maybe a bit better R-22. Problem I would think is using a large case in the 7mm mag and a smaller case on the Creedmoor.

Use RL-22, I use it in a 243 Win, 260 Rem, 280ai and a 300wm as a powder of choice.

rl26
rl23
h4350
rl22

Either 4831 variety
Reloader 19
Reloader 23