I have taken my KSC USPc to AirsoftDepot and TorontoAirsoft. neither could assist, as they didn't have the parts for the hammer assembly. the problem was that the hammer wouldn't fall most of the time in single action. double action works fine.
there appears to be something wrong in there, perhaps a worn part is what they told me.
I'm wondering if anyone can assist, in the GTA who may have spare USP parts.