Thanks for the suggestion, already checked pin diameters before I even put the new upper together. You can literally look in the pin hole from the left side and see that the receiver is I'd guess 1/64" or less from going all the way down and you can see the bottom of the pin hole on the upper isn't low enough. And taking the striped receivers and look at them from the sides with the light behind it and you can see the spot that it hits, not very much and not real long a spot.
I'll be truthful with you have haven't done any serious AR work in better than ten years. This is actually on my own personal gun which I had another A1 upper on when I got it. That was well I guess a while back because I converted the A1 upper into a flattop before the AWB of 94. All that was available then was converted upper where they cut the handles off and pinned a rail on them. I went a slightly different route and found I guy that knew how to weld on T7075 aluminum and had the rail welded on.
I know what I have to do, its hitting on the rear corners of the upper as you look at it from the side about a quarter inch up. Trim it down slightly and it will fit and lock up quite tight. I ran into this once before with a varmint barreled flat top I built for a guy back in 97. Both DPMS upper and lower and it took just a couple thousands off the back corner and it fit tight and ran like a charm (shot under 1/2 MOA out to 200 meters too. That gun shot well!)

