I think Jim Watson is right about not having enough to rebore to a .257 Here is link
Here is another the old LaBounty reboring with new owners
I've had only one barrel rebored it was done by LaBounty in 308 Norma mag and it was chamber by him.
Most custom barrels can be made to match existing contours and length and you have to weight cost of new barrel vs reboring and where you save is having rifle rechamber by who's doing the rebore.
Mine was done in the 80's and I had better accuracy with the rebore and here is something from the Clearwater on accuracy
What kind of accuracy can I expect?
Each barrel leaves our shop with a bore that is consistent in diameter and twist rate with a fine hand lapped finish. These are two traits of many that contribute to accuracy, and the only two over which we have control. Reboring will do little to straighten a crooked bore (although some crooked barrels shoot pretty well). A bolt action that has an out of square bolt face, crooked barrel threads, only one bolt lug bearing, poor bedding or any other problems known to cause poor accuracy will not shoot very well even with the best of bores. If you are considering a rebore to correct an accuracy problem it is wise to eliminate as many other potential causes as possible before reboring or rebarreling. A gunsmith familiar with action accurizing/blueprinting techniques can identify and correct many problems. This will allow one of our rebores (or any good barrel) to shoot to it's potential. With this in mind, you may expect your newly rebored barrel to shoot as good as when it was new, many times they shoot better and almost always foul less. Performance equal to the better cut-rifled aftermarket barrels is common.