APM RM,
There's barrel life and there's barrel life. Peak accuracy may start to go in a high intensity cartridge barrel in under 3,000 rounds, as with the .220 Swift. I've known users of this cartridge that swapped barrels at 2,000 rounds or so, as the bore to case capacity is very high and the barrels erode quickly. With a .308 I would expect around 5,000 to 7,000 before peak accuracy failed, depending on the barrel steel and type of rifling as well as the loads used and the type of fire the rifle was subjected to. Then there is usable accuracy, as most military surplus shooters know. This means that 1 MOA or thereabouts may not be attainable, but deer accuracy to 200 yards is still a reasonable expectation (call it 2-3 MOA). From inquiries to the various manufacturers in the past, when I did a lot of NRA "High Power" and "Military Match" shooting, the usable barrel life for a .308/.30-06 was considered around 7,000 to 10,000 rounds. I was told that chrome plated bores and various barrel alloys could extend this to 15,000 or so in a .308 type cartridge. I once owned a 7x57mm surplus rifle that had only a hint of rifling in the barrel when I got it. It shot a consistent 3 MOA for about 1,000 rounds, and then it just started keyholing and groups opened to scattergun like affairs.