Your 1187 is a fine choice for waterfowl hunting. I prefer IC choke for most of my waterfowl hunting. Shot size depends on many factors, size of birds, distance of shots time of season. I would agree with earlier post 4's for small birds 2's or even 1's especially late in season on larger birds. Use the time now to test a number of different brands and shot sizes to see which work best in your gun. A couple of afternoons at the range and patterning board can pay dividends come fall. Good luck.