Accurate mag

When I first got my Accurate mags I could only fit 9 in. I loaded them up with 9 and let them sit a day or so to let the spring compress. I can fit 10 in fairly easy now. Also make sure you're seating the back of the round against the back of the mag. I feel that helps as well.
 
AI mags are like that. I have a couple that get 11 but a couple that can only get 10.

.308 and 6.5 Creedmoor use the same mags so no difference as far as capacity. If you can only get 9 then maybe take it apart and look inside the mag body or spring for any issues. You should be able to get at least 10.