Sounds like life expectancy for somebody using a .243 to throw 100-107gr slugs at 600 yards and beyond. The 6mm is a darling of the accuracy and match rifle crowd, but most of the cases I can think of being used are quite a bit smaller than the .308-parent case of the .243 Win. (I know of one 6mm AR in circulation at the local Highpower matches, and a 6mm XC.)
Anyway, don't shoot lots of rapid fire strings and don't firewall EVERY load you run through the rifle, and that barrel will last a long time. Or get in the habit of the match shooters I hang around, and figure a rifle barrel is like car tires; when they're worn out, change 'em.