My older Mossberg 500a was not always extracting 100%, I took it to a good gunsmith, he told me that the 500 pumps can have this problem, and it is a "design" flaw. It was is not the extractors, but the small cuts in the barrel where the extractors fit into. The left side extractor was rounded off a bit due to the tight extractor grooves in the barrel. The gunsmith milled out the extractor grooves in the barrel and touched up the left extractor and problem solved. No more fail to extract.