Top Receiver: Plastic with metal catch.  The plastic on the to receiver isn’t too bad compared to the fore grip (but I sprayed it anyway).  The detail isn’t as good as I would have liked, but it’s good enough.  The top receiver is also the top of the mag and flicks up on a spring loaded front fixing.  It’s held down by a small metal catch, which is another oversight by TOP.  The catch is designed to slot into a hole in the receiver but you have to pull the catch out a bit to get it into the slot.  This is not a huge problem but it could have been so much better.  I have solved this problem with a small block of plastic under the top receiver cover and the spring of the catch, works fine now.