RE: mossberg 935 jamming probs.
One thing I have found is semis do not like alot of oil in the action and only very light oil at that. And no oil at all on the gas tube. I see people load it up in there, and when the gases come back, that oil just sucks up that fouling and turnes into grease and grease in real cold weather causes jamming.
Just keep the outsides and inside of the barrel oiled. Anywhere the gas operation is happening, keep oil out of it.
If you have to use oil, use light rem oil. And no WD40 allowed near it.
My brother had a chambering issue. He sent it back to mossberg and they took care of it.
My suggestion is take it apart all the way, use rem action cleaner or even brake cleaner and get all the oil and gunk out especially on the bolt and firing pin assemply and gas operation. Now put a light coat of oil on a rage and wipe the inside of the action out. No more than that. No oil on the the part where it holds your shells or in that area.