I got my SumToy 562-3 for an Ithaca Model 37 TurkeySlayer in the Mail today. I ordered it on Wednesday morning. That is some great service. What are the reasons for the rings and grooves in the ID of the choke? I was expecting the rings from speaking with William, but not the grooves. I hope to pattern it next weekend. I have Hevi 13 5 shot, 6 shot, 7 shot, and Magnum Blend to test. From what I have read, 7 shot should be the one.