action jams

Hello revolver aficionados. I got a Pietta Great Western II Californian a little while back. No sooner than I got it and off it went to EMF for warranty service. They fixed almost everything wrong with the gun, but something still seems to be amiss with it. When I cock the hammer (four clicks)...

When shooting the UPPER barrel, the action "Jams" and is difficult to open. Lever lock is fine, smooth; the fired shell shows "some" small firing pin drag marks in primer. Have polished firing pins, etc and they are smooth and free. Action does NOT jam when snapping on empty chamber; either...