Lets start with the rounds not fully chambering....
Is you chamber bright and shiny? No sign of anodizing?
Have you tried any other ammunition other than Corbon?
Seems to me, a while back Corbon put out some out of spec.
Is there anyone near you that has one of Marty's chambering
Dies to check the ammunition?
If you can't easily chamber and eject a loaded round, your rifle
isn't going to function properly. If all of that works, then it's time
to check buffer springs and gas blocks.