I had my M7600 (.30-06) rebored to .338-06 years ago, and it turned out great. No changes were needed to the magazine or bolt face of course, and feeding is perfect. In this instance, unless you do not reload the longer case makes more sense. You can load it down to .338 Fed velocities, or up it to full .338-06 speed. For the .338 Fed you'd need to use .308 magazines - no problem getting those of course.