A tightly machined upper (perhaps a little too tightly) - Icon Defense Forged Stripped Upper Receiver

Mated this upper with a Icon lower receiver, and the fit is tight with no rattling. So tight, in fact, that I had to file off a little of the surface on each side of the rear takedown lug in order for it to open/close without force. I also had to open up the rear takedown hole a hair to get a mil-spec takedown pin to fit through it smoothly, otherwise I was having to hammer it in and punch it out. The barrel extension also had to be thermal fit, but that applies to many uppers these days.

It is a very well-machined upper, however I think the surface finish might be a bit too thick which caused the binding issues I encountered. This only stacked with the similar lower receiver tolerances. This being said, I would much rather have to remove material than have too little from the factory, as one is fixable and the other is not. For the money this upper costs, I believe the finish thickness could be improved so that this issue does not persist, especially when used with other Icon parts. It doesn't do anything that a lower-budget upper doesn't, but has a nice finish and shouldn't have any issues with wear for the foreseeable future.