If you have a carrying handle laying around put it on the upper. Then turn the whole thing upside down and see if there are four points of contact. Also make sure what you place it on is flat and true. If there isn't then there is a problem. On a brand new upper you should have all four points touching within a few sheets of paper. Also when you set the upper down flat how does the front sight base look? You paid money for it so it should be right.
Dan




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