A couple things come to mind:
Was this all with one particular magazine, or did you try with more than one? Which mfg. mags?
With an empty mag in, do you feel any rubbing on the bolt/carrier that isn't there when the mag is out?
I would encourage you to try with other mags just to help troubleshoot.
I'm overjoyed with mine, I am sorry you are having trubs. I know it sucks right now but I am SURE they will make it right by you.
Keep us posted.