Need more info than that. What kind of 12 gauge? How far are you wanting to be able to shoot? Are you shooting factory full choke, or an aftermarket turkey choke? How much are you willing to spend on shells?
buy some cheaper turkey shells and see how they shoot first, so you don't blow a lot of money patterning your gun... winchester double x, federal turkey thugs, etc. Shoot some paper and see what the patterns look like and don't shoot a bird too far for your gun to handle