[Oldnamvet]

I was reading that in the old days of blackpowder, people sometimes would not clean their rifles as much as needed. So, once a year, they would show up at a gunsmith to have their pitted and rusted barrel "freshened out" or bored out a little to make it like new again. The gunsmith would provide them with a new bullet mold for the barrel and they would go off back to the mountains.
Can this same thing be done for modern barrels? Could someone with a heavy barrel in 6 mm get it reamed and rifled for 6.5 mm? Or would this cost more than just buying a new barrel and having it installed.

[Old Fuff]

In both theory and practice what you suggest can be done, and sometimes is when someone wants to preserve the markings or whatever on a classic or antique barrel. But since you have to remove the barrel from the receiver, bore, rifle, and rechamber it, you usually won't see much if any cost savings over fitting a new barrel.