Anyone can make a lemon, I've seen it with every brand to include Colt, DD, Noveske and even KAC. Funny thing is that you sent your upper back, it was replaced and then you listed it for sale before even checking to see if the new one was better.
I have built several uppers using the SS410 barrel and all of them were sub-MOA. Several other people in the thread you linked to, also stated that the groups were not normal and they reported good results.
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