Heya bud,
All good advice up above, but one additional q.
If you load up a single round in the mag, what happens when you fire? Do you get extraction and does the BCG lock back?
I had the same issue as the OP with a V7 DPMS BCG and it was an out of spec extractor. Talked to V7, they confirmed my findings and sent a new extractor, that problem was solved. Contact the company and tell them what's going on and they should fix you right up.