Chilean 1912 Steyr 7.62 Nato Mauser need Help

Need More Help/Info Please, I have the supposed re-bored/chamber insert ???? 29 inch long barrel, like new condition with great bluing. I cant see the " insert ". Could this actually be a NEW barrel ??? Also, can I safely shoot 308, I dont understand why it is so much more pressure than nato 7.62X51, they look to be the SAME in size cartridge ????, Thanks Much Guys