Best case he re-chambers the barrel and perhaps it shoots reasonably well. Less best case he re-chambers the barrel and accuracy is mediocre. Worst case the re-chamber job goes South and he's out the $ for the reamer, the barrel is ruined, and he is back to needing a new barrel.
I've never been fond of cutting extremely hard metals if it can be avoided at all cost, and this seems pretty straight forward to avoid.
