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.