Helping a buddy with his build. Test firing rifle and does not cycle. Swapped his BCG for mine and fires fine. Only thing I have found is when bolt is rotating back it has quite a bit more drag than mine. Now his is new and mine few hundred rounds used. Pulled it apart and cleaned,reassembled and same thing. Not sure who's BCG,was bought as complete assembly. He bought from few different sites against my advise.
Ideas?