You were so certain you'd "discovered" the absolute BEST way to get carbon out of a bore that a number of people apparently didn't want to answer, for whatever reason.
My experience involves prepping a number of bores down to bare steel for installation of Dyna Bore-Coat since it was introduced over 15 years ago. It requires the bore to be absolutely clean, and the fastest method I came up with after some experimentation was around 20 strokes of a tight bore brush wrapped in a cotton patch, then slathered with JB Bore-Cleaning Compound. Would be willing to bet that's quicker than a brush and Kroil, since I also have considerable experience with Kroil. The JB method takes about three minutes--and eventually became part of the directions for installing DBC, which is highly effective in preventing carbon build-up.
At least a couple of people also suggested highly effective carbon cleaner/solvents.
For also curious about what kind of scope you have on the rifle you used to shoot the half-inch group at 50 yards.
