All guns are different and I can only speak intelligently about mine but sounds like identical problem to yours.
1. Only did it with 3 1/2"
2.Barrel was seated tight ,barrel nut very tight.
3. Chamber deep cleaned and polished.
4. Didn't exhibit problem until about 4 years old...bought gun new....Low round count turkey gun, some goose hunting.
5.Brass swelling at base near Tim causing the hard extraction.
6. I took micrometers and measured the receiver end of chamber opening thinking it was machined improperly....it measured exactly same as my brand new 935 which functions properly.
7. I would have liked to try a different barrel but was disgusted and gave up on it.
8. I did send my 935 back to Mossberg for a problem when new and it took about a week turnaround....pretty quick.
I think as someone else mentioned maybe try a friend's barrel if you can to see if that helps.
Good luck I feel your pain.
