Hold the conclusions. I'm afraid I have presented the results of a botched test. When I finally got around to cleaning the bore I found it badly leaded. After generous application of steel wool, lead out and elbow grease the bore was clean but what do you do with test reports partially obtained with a leaded bore? Probably do the test again.
I now think that the bullets I dug out of that drawer were probably from a year ago last September when I was bore cleaning after every target card at the 2017 NT to avoiding loss of accuracy. Should have thrown the left over bullets away.
By looking at the group sizes with this new information the two good groups followed by much bigger ones, in both CB strings, take on a different light. Full charge JBs will clean out lead giving the CB string after the JBs a fresh start.
CBs after: 1.06, 0.78, 1.84, 1.86, MOA -- Average 1.38 MOA
If I had only fired two CB groups before the jBs and two CB groups after the results would have looked like this:
CBs before: .90, .64, -- Ave. =.77 MOA
CBs after JBs: 1.06, .78. -- Ave = .92 MOA
Still looks like the JBs didn't improve accuracy, but only 20% worse and based only two 5-shot groups for each condition -- still, a strong hint that accuracy was degraded.
I will find some bullets that fit better and produce strings of groups that don't grow and try again.