I recently purchased a mossberg 835 ultimag for turkey hunting. When ever I pump the gun slowly to put a round in the chamber nothing happens. The bolt closes but fails to put a round in the chamber. But whenever I pump it fast it performs flawlessly. Is there any way to fix this or is this how it is supposed to work?

I'd imagine that's how its supposed to function. In general, gun designs tend to make use of inertia...trying to slowly cycle a round takes that out of the equation. (No, not completely for all you knit-pickers). Is there a need to slowly cycle the round?

Is a shell feeding into the receiver but the carrier not lifting it up in front of the bolt or are no shells moving at all?

It sounds like you aren't fully pulling the forearm all the way to it rearward most position so the interuptor releases the next shell to the carrier.

what bb said is pry the case. i had this trouble when i very first started to shoot but i just thought about it for a little bit now it not a problem.

my 835 does the samething but to me its not a problem I actually like the fact is does this, because sometimes when im hunting I keep a couple different loads in the gun in a particular order. Usually my first shell thats in the chamber will be a #7.5 shot field load then my next two will be high brass loads with #6 shot I do this usually when quail or pheasant hunting my first shot will be on the jump not needing a heavy load if i miss the next two high brass loads will give that extra power for the longer shot as the bird is flying away. but if for some reason i need to take the shell out of the chamber I can without the next shell jumping into the carrier, for instance if I wanted my first shot to a field load with #6 shot instead of my usuall #7.5's I can easily swap it out with out my highbrass load loading into the carrier and interfering with what would be a quick load swap.