I have found that quite often, failures to EJECT (when extraction is fine) can be traced back to an overpowerful extractor spring. The extractor pushes the case hard against the oposite side of the bolt face, so the ejector can't push it out of it's recess in the bolt during the cycling of the rifle. You can check this with an empty case and your bolt. If you hook a case inside the bolt recess, and it easily flies out when you release pressure to hold it in, you are probably OK. If there is ANY hangup getting the empty case to be flipped out of the bolt by the ejector, then check try reducing extractor pressure. Also insure that your ejector moves freely inside the bolt.
If the ejector and extractor work right, then I would start looking at the rifle having too much, or not enough gas into the system.
Check bolt rings, the gas key on the bolt, and of course the gas block and gas port from the barrel. On rare occasions, people get goop from cleaning their rifle into the gas port and it clogs up the port. Usually a good blast of gun scrubber through the gas tube will clear stuff out.
