Spinkiller -- how many times have you chambered the factory rounds. The bullet will jump forward a few thousanths each time. Do the rounds still measure 2.23" in overall length. You may be jamming the bullets into the rifling which would make them hard to extract. Just a thought.
With the upper removed from the lower -- can you move the bolt back and forth in its travel easily -- without a cartridge of course. Keep the charging handle locked and you should be able to move the bolt carrier group back and forth -- locking and unlocking.