I take it that this is a new rifle. So, first off, you're gonna have to soak down that bolt carrier. These things like to run really wet when they're in their break-in period. Wet, as in they'll sling oil as you're shooting them. I usually give my carriers a mobil 1 bath overnight for new builds. Pick up by the bolt, and sling the oil off it, dry just the face of the bolt, then drop it into the upper receiver. That might help you out.
The other possibility is the chamber could be a little tight. If it runs fine using 308, run another couple hundred rounds through it before trying to go back to the M118.
Just a couple ideas to get started. Others will be by to pitch in.