Very slight movement (almost imperceptible) is normal. A wobble is not normal! Quit parroting crap you've read on the nets! It's normal for ragged out M-16's that are in dire need of replacement. Only you can tell what's too much. Go to your local LGS and handle several complete AR's. Do they feel as loose as yours? Are you satisfied with your product? If no, then send that crap back and make them do it over! If it were me and I just shelled out close to a grand for an upper, it better be tight. Yes, functioning is paramount, but it should actually fit as well. If shrubmaster and boulder strewn waterway can get it right, then DD damn sure better step up to the plate at the prices they charge. JMHO, do what makes you satisfied. Oh...in before some noob tries to put me in my place by saying that it's the normal state of affairs (since he read it last month on the nets). Get bent! It's not your money! The O.P paid the money and he should get the rifle they should have sent him in the first place. Daniel Defense is a respected, well thought of company and I'm sure they'll take care of you. I almost pulled the trigger on a DD a short time ago. They are nice! Good luck O.P.
Konger