I'm guessing what you call "semi clean" is the same as me, you fire off a couple of primers on a clean barrel. I've tried my TC on a spotless cold barrel. If you remember a while back I did a cold clean barrel grouping test. Had a little over an inch 5 round group at 150 yards cleaning the barrel thoroughly and cooling it then popping 2 primers, load and shoot. I also tried it on JUST the clean barrel. Groups opened up considerably and were inconsistent in elevation but I didn't experience windage issues. Only elevation.