Rereading his posts it doesn't seem to me that he has changed his patch thickness. But he's darn near tried everything else.
Maybe its just a bad barrel. One in a million but a bad barrel just the same.
Could be a ';bad' barrel, BUT - he needs to test with a real patch. By that, I mean that I do not consider .012" to .015" thick patches as real patches. 12 to 15 thou. is not thick enough to use as a cleaning patch, let alone expecting it to shoot well and seal as a 'target' - shooting patch.
10 ounce denim might change the accuracy entirely. Even 8 ounce that I measure at .018" might work, with bore size only about 2 thou larger than the balls.