When, I sent mine back for these same problems, I asked them to replace the Slide, barrel and ejector. I do really believe it is a combination, of the breechface cut and the barrel chamber tolerances.
The funny thing is, I know it will come back saying they replaced the extractor. If I go out to the range and it is not fixed,I will be extremely pissed! Let S&W put 200 or more rounds through it before they send it back. Why should I have to go to the range and spend $75 to "test" their work??