I was wondering if that Rossi has a choke tube threaded barrel - if not, and if you want to use that shotgun, you will probably need to either have it threaded by a reputable gunsmith or buy an extra barrel just for turkey that is (or can be) threaded. As the others have stated, a Modified choke won' t constrict your shot charge satisfactorily for turkey in most normal ranges (in any guage). Using a Modified will result in some kills, but you will likely wound and lose more.

I don' t know squat about Rossi shotguns, but if you are determined to use this one, I' d be scouting for a dedicated turkey barrel for that particular shotgun and once I had one I' d be starting my patterning at 15-20 yards with actual kick-ass " turkey loads" , and be working my way out from there. Best of luck.