The duds from the first batch have all been accounted for, unfortunately some more duds have been found in later batches and I don't think anyone is sure what serial numbers these are. Myself and a friend of mine both got "duds" back in February, but now they have been replaced we are both very impressed with the strong reaction of this ball. The only way to resolve this issue is to speak to Dynothane who have been excellent in dealing with any enquiries.