No one can accurately tell you the best shell for your gun and factory turkey choke combination without shooting your exact setup with many different shells at the distances you typically shoot a turkey at to see. That will get costly quick. Each gun and choke and different barrel lengths will make for varied pattern results and sometimes even different point of aim, point of impact results. With that said, a dang good shell for the money is the Winchester High Velocity Turkey Loads (black shells). I shot the 3.5" #4s for 10+ years with great results. A box of 10 3" HV shells will cost you about $13 with tax. I'd recommend you start with the 3" #5s and see how they pattern at 10, 20, 30 and 40 yards with your setup. Make sure POA/POI is the same. If not, an adjustable sight may be needed. Rule of thumb for maximum effective distance should be 40 yards and less. Best of luck this turkey season.

http://www.cabelas.com/shotgun-ammuniti ... oads.shtml