Imp.Cyl. if a single barrel, Imp./Mod if a double. Short barrels 26" or less. Use high velocity 7's or 71/2's shouldn't be any circumstance where you feel wanting. If the hunting terrain is really wide open,no brush,to speak of have used plain modified in a single barrel with fine results. Best commercial shell in my experience Fiochi Golden Pheasant 2 3/4's inch, 1 3/8th's nickel plated 7 1/2's. I assume hunting over pointing dogs, if flushers or dogless, I might tighten up on chokes a little. Your personal choice of 20 or 12 gauge. This combo has served me well for 35 years. Pattern your gun and pick what you like.