The threads are enough smaller that it works. But they're also enough smaller that even with a sporter barrel taper, the whole shank can be cut off and still have plenty of shoulder. Better to start fresh with a really good chamber. Mine has a 700 sporter barrel done this way almost 20yrs ago. It shoots very well.
****Addition. Some of the shank was cut back, not the whole thing. Just enough to get the reamer into fresh metal for a new and very minimal chamber.