I have some bad news for you. I realize the .308 doesn't burn as much powder as some other cartridges but I doubt you'll see the kind of barrel life you're talking about, at least out of an unlined barrel.A chrome bore will keep it's accuracy much longer than a non lined bore.
Lets say you have two .308 rifles one lined and one not.
They both shoot about 2 MOA. The unlined bore will start to lose it's 2 MOA ability from about 7 or 10 thousand rounds.
The chrome lined rifle could still be shooting 2 MOA at up to 15 to 20 thousand rounds.