There can also be changes to the bores interior dimensions but there doesn't have to be. The problem many don't understand the difficulties with turning ANY barrel. Of course all barrels are turned at some point so it is possible, it just requires some common sense practices. The centers used should be spring tensioned, at least one. The material should not be rushed and coolant is needed. We must keep the barrel from developing pressure lengthwise or it will surely warp. The interior dimensional changes take place when too much stress is placed on the barrel by the bit. It's one of the reasons Walther leaves that little boss on the muzzle end of their barrels, the other is weight distribution. It would also be possible to flute the barrel to remove weight. Even to reduce the corner to corner dimension AND flute between the corners to reduce even more weight. You must be cautious about removing too much metal and making the barrel unable to contain the pressures it must but a lot of weight can be removed on most barrels. Good luck!!
