This year I've bought four b-barrels, three brands, and none required a break-in. They all were accurate and smooth enough right out of the box and didn't seem to change over time other than typical wear/tear.
Here's the latest example, first 10 shots (20y, benchrest) right out of the box, zero adjustments. Didn't even clean it.
Perhaps that's something which used to be more true yesteryear. Or it could be an urban-legend, I've yet to see any concrete evidence of it helping. Even with a modern powder-burner. I wonder if there's something besides anecdotal evidence.
Anyway, my two cents. Besides, why aren't you just shooting it? Surely you can come up with a few feet somewhere to play.