Thanks for bringing this thread to life, I need to recrown a QB78 that I recently bought and was dropped on it's barrel crown during shipping. The gun has shot like a shot gun ever since.
Unfortunately, these days many gun manufacturers put an off center countersink on the crown, to make it even more delicate to possible fix it. But a good method to just remove some burr.
One thing he did not do is run the drill in both directions. You need to deburr both sides of the rifling.