Will it extract a loaded shell? Does the extractor/ejector lift when there is no shell in the chamber?
If so I would polish the chamber on it. I've done a few single shots that would not extract/eject and polishing the chamber done the job.
Your shotgun is supposed to have an extractor not ejector. It does however have a spring.
Don't know if you been here or not but here is a link to parts and schematic. Numrich Gun Parts Corp. - The World's Largest Supplier of Firearms Parts and Accessories