I'd verify that when feeding, the case rim is slipping up onto the bolt face UNDER the extractor as it should. Then if that's not an issue, I'd make sure the locking lug recesses are clean and free of debris. After that I'd clean and lightly lube the locking lugs with some good grease.
I do have a question, though: if you chamber a live round and put the rifle on safe, then open the bolt and extract the cartridge only an inch or so and then close the bolt again on the same cartridge, is there any difference in the feel?
God I am hating caliber threads more and more