Just picked up a new A2 upper and when I assembled it, the mags wont fit. I have a known good upper and lower that I have fired many times... so out of 3 lowers and 2 uppers being put together in all combinations, I have determined that the new upper is the problem The mags fit into the lower no problem, all mags the same. But then the new upper is locked in place, the mags dont go in all the way, if I force them they will stay but do not click into place at all. I mic'd the width of the uppers and they both seem the same but with one upper assembled everthing is fine, when i put the other one in... mags dont go. Even removed the bolt from the new upper and I have the same result. Anyone seen this before? I am unsure if I can take it back to the guy at the gunshow... is this something that I can dremel into submission? thanks!