Run a search on Mossberg 835 and I think you will have many threads that ask the same questions.

Anyway - their factory choke is a pretty decent choke and will get the job done. If you can afford an aftermarket choke - I believe your groups will greatly improve.

Mine shoots best with a 3 1/2 shell. #6's from Remington but I plan to try some of the Winchester HV this year.