What is the best way to finish the upper rails on a bent flat to make sure everything is true and square? I was looking at some 100% receivers today at the columbus gun show and I liked the way the rails were cut. Just looking for some input here, I am having trouble seeing the forest for those damn trees.

The most important thing I can tell you is to take your time.  There is a nifty accessory some of these guys have for the dremel tool that acts as a depth stop, to give you a consistent cut down your rail.

I just took my time with my dremel tool and a few cutting wheels.  I found it was easiest to make the start of a cut all the way along the rails, but not all the way through.  Then check to make sure it's straight, then cut more and more until you have the upper rails trimmed.  Use a good file for the remaining tight spots after you check the fit of the carrier.

I tried a Dremmel and worked too fast and sloppy and messed up the $35 receiver. I bought one of the Harbor Freight Milling machines, I hope that helps with my underfold that I still have to do.

The fixed stock receiver is trash, so I think I will fold an 80% Tapco flat and try to modify it. If it don't work it is jus another twelve bucks down the drain.

The best way to finish the upper rails is the way they do, on a milling machine.

I cant afford a milling machine , although I do think that would give the best results. I definitely need to check out that dremel depth tool . I think that if I take my time with it I can produce something pretty close. Thanks for the ideas guys.