Gale, may I pick your brain on a question I have been wondering about? It has nothing to do with bbl break in, but this is as good a place as any to ask it.
You mentioned above that JB, and I'm sure other compounds or cleaning methods (I think the 'tornado' brushes are a plot by the factory bbl manufacturers), will wear down the sharp edges of the rifling. My question is how important is the sharpness of the rifling to accuracy. Have you done any experiments with sharp vs. dull rifling, all other aspects of the bbl being equal? Maybe this type of examination would be a better test of when a bbl has bit the dust instead of throat wear, for instance.