Here is a more drastic example, a 308 barrel, with 8000 rds... the whole chamber area was cut out as shown here, to get to the less firecracking in the new 30 RAR chambering from a rem 700 bolt, to an AR 15...your project will be much easier, for a gunsmith. If the barrel shank is long enough, the rifling good, .maybe set back a quarter to one third inch to clean up the old chamber...depending on reamer drawing of new cartridge reamer, to the orginial 338 Lapua chamber.