I have a dedicated upper...it's excellent now but it didn't come that way out of the box. When new, I couldn't put a string of more than 3 shots together. I tried to get it to cycle myself but ultimately gave up my workarounds and just called NEA. Their service Dept was great...took the upper back and swapped out the firing pin (original was too short) and installed a new barrel extension. Runs like a top now.
I use both Black Dog and the included IMI mags.
My advice...if you get / have one and it isn't cycling, don't waste your time trying to fix the issues...contact NEA and let them fix it. Was a PITA at first but now that it's fixed, I enjoy it alot.