Psychodog,,,,You might want to have a smith really look at that barrel with a good bore scope....When I got mine for Christmas and, like a little kid, started checking all my barrels, I was especially interested in my .308 semi-cuastom that had been giving me fits in the accuracy department..
Approximately 5 inches past the chamber, I found what appeared to be a stress crack running about 3/4 of the way around the inside, but wasn't visible on the outside...I took it to a local smith and just asked him to see if anything was amiss, since I was having accuracy issues and within a couple of minutes, he came up with the same observation...
While that doesn't explain the lack, or odd, pattern in the exit marks...There may be something going on away from the muzzle....