To be honest, we/the crunchies were pretty brutal to the point of ruthless in our cleaning regime especially with machine gun barrels to the extent of using hardened steel* wire gauze to scrub them until they were shining....... But their barrel life was a speedy 10,000 rounds or so - or less if the gun or SF crews were using up the remaining ammo on a Friday afternoon.......
But the rifle barrels weren't subject to such harsh treatment. They remained good until the end all with a strict(?) supervised cleaning regime for several days afterwards. That's my experience. And the barrels lasted until the gauges or range tests said '....no more'
* don't believe it? Just take a new piece and look at the blue hardening and quenching colour around the edges