In the non-aftermarket category, get ready to Dremel a pretty substantial notch in your feed ramp (if you have the basic B-14 HMR, not sure if it's necessary on the Pro models) or take it to a gunsmith to have them do the same. I loaded up a batch of 6.5 CM rounds for an OCW test at 0.020" off the lands and quickly discovered they won't feed from the magazine (Begara factory, PMAG, or MDT) because the bullet tips get caught up under the feed ramp and nose down. As others have mentioned on here, this is a pretty serious design flaw that has to be corrected if you want to shoot long, heavy bullets seated out to where they need to be.
Aftermarket wise, a new trigger, MDT metal magazines, and a KRG Arca rail (very easy to put on) are some good upgrades. The rifle can shoot wonderfully, just needs some clean up around the edges.