1st time posting here. Hope you can answer some questions.

I've been told that the 300winmag is overbore for 30 cal & will burn a barrel out sooner than a 308 win (which is considered a very efficient cartridge). If this is the case, can I expect to get better barrel life from a 338 RUM when compared to a 300 RUM? Is the 338 RUM considered overbore for a 338 caliber? What is the most efficient cartridge for 338 caliber?

Thanks in advance.

Chris.