The bullets could be plated with copper - a fairly simple electochemical process which can be redone as needed.
The barrels have always been a problem with very hot loads and high velocities. That is what discourages me from buying a 300 magnum of any variety; I'd have to get several spare barrels. Can the barrels be made out of a much more erosion resistant metal? Tungsten? Yes the barrel would be expensive, but it would stand up to hot erosive loads for forever.