I heard the US machine story but also have never seen a real source - just quotes of this real source but never the actual source. What I went on was that Walt Kuleck and Clint McKee made the claims of the proper forging of the Polytech receivers. There were also people doing well at matches with them.
There are gunners and people who like guns. Unfortunately, I'm in the second group. I brought this rifle to the first of two CMP matches and mostly hit the paper but badly. The local gunnie there, an ex-marine sniper tried it and thought it was great. He found my match ammo poor and tried some of his and proceeded to do a bunch of 'X's at 200 yards.
I know the Chinese were (and are) big in the fake market. I have some of their M1 carbine ammo that has the headstamps looking exactly like Lake City. The story I heard was that it is corrosive and was going to be packed like CMP LC but they got caught and it was imported in Chinese boxes. Another story with no real source.