I have the same barrel, load the same round, same charge and.......same result. My barrel is a copper mine. A look down the muzzle with my endoscope camera after 10 shots and it all copper. A close look at the rifling and it looks like the teeth of a gear.

If I'm going to continue with the 6.5 CM, it'll be with a new Criterion or Shilen barrel from NSS.