he's looking for an upper receiver. with a bcg or no? I don't know what they would be used but I think you might be better served buying new for a hundred dollars or so more. I have used model one sales for this before and I very happy with what I got (24" ss heavy barrel flat top, floating hand guard low pro gas block). It shoots very well, I hit a uspsa head at 600 yesterday with, get this, a 40 gr v max yesterday. Only once, but I only tried once. I got a kit for around $550. Good luck.