Not much. Rib , Stock , Recoil pad are some of the more common differences...but some of these features are shared somtimes as well.
Found this on another site...|
The only real difference between the 391 field and Sporting models are the rib.....narrow and parallel on the field and tapered front to back on the Sporting. The sporting model will sometimes have nicer wood also, but that varies gun to gun. Both are 3" capable. You should acertain whether it is a newer OPTIMA BORE model or not.....it will have the word OPTIMA in the forend and it would say so on the barrel. They have been made, originally without the Optima BOre Upgrade, then they changed over to OPTIMA a couple of years ago, and now that is standard. The OPTIMA bore treatment is considered a bit better, but not a deal breaker. Basically, if you get an OPTIMA bore gun, you need BERETTA OPTIMA Chokes, or aftermarket chokes for OPTIMA....easily obtained.[This is assuming that you might need additional chokes].
If its not OPTIMA, no worried either, then it takes BERETTA Mobile Chokes, which they, and most all aftermarket companies make also