Take a look at Wrights Superior Chokes "Swarm" tube for the 20ga. It has won more Turkey World Championships in both the 12ga and 20ga than any other tube out there. They were using Hevi-Shot 13 factory shells. Plus, were u using the regular Hevi-shot or Hevi-13 shells? Big difference!!! I have a 11-87 Premier with a Swarm Tube and scope and a 40yd shot is nothing for it using 6's.