Well it turns out that the new Ballistic Advantage BCG has some kind of an issue, perhaps with the extractor judging by the marks it puts on the rim of a case (kind of like it is just ramming into the rim without slipping over and engaging it). The DPMS BCG works fine in both uppers and the BA doesn't work in either. Fortunately, BA is being great with their customer service and has shipped a replacement without even waiting for the return to arrive.