Back in the 1950's and 1960's, there were a number of barrel makers who would ream/re-rifle a barrel out to a larger caliber. One of the most common was taking a shot-out 30/06 barrel and reaming it up to .338/06. You almost never hear of anyone doing this these days. Depending on the quality of the new barrel, a complete re-barrel is going to cost you in the $325 to $450 range.