Anyone who is giving any advice that is not specifically focused on the extractor/extractor spring, is not giving advice. The bolt carrier group is cycling, so lube, gas rings etc. are not the problem. It could be the ammunition, the coated steel case stuff can GLUE itself in the chamber, most common in a very hot AR. I would (and have myself) change the extractor and spring, it should and has cured my nonextracting AR. Of course all cycling/extracting problems would be just unpleasant memories if you trade your AR for a SIG 556.