I've been watching this from the sidelines for several days now and I thought I'd chime in with some relevant info before this got too nasty. If you go and find the various videos that Brownell's has put out, they discuss why Pmags do not fit. Between the bevel on the sides for the modern angled magwells and the built up section of the front of the mag to help accommodate the internal curve, they could not make it fit inside of the profile they established to match the old lowers. I suspect they would have had to make the front of the well too thin. One way around this would be to mimic the massively angled magwell cut of the prototype sporter model, but it's hardly the 'iconic' model of AR-10 that they are going for. Also, if you keep up with some of the updates they've put out, the bolt carrier is getting the three vent holes that are so prominent on the originals.