My 2nd Maccabee reciever set is on its way back to Maccabee because the mags bind in the upper. Take the upper off and see how the mags fit in the lower by itself. Then put the upper on and try again, but don’t tighten down the bolt. It made a difference on mine. Contact Maccabee, he should be able to fix it. It’s probably the feed lips hitting in the same spot as mine.
My first set was exchanged by CSC because it was missing the spot for the charging handle to latch onto.
Maccabee seems to have taken a page out of BCL’s playbook on how not to do a product launch.