most barrels for example like 308 that have a good barrel life, to barrel burners, typically can only shoot bullets continuously for 5 to 10 seconds as the bullet is only in the barrel for .002 seconds... usually the speed of the bullet and how HOT the charge is what will effect the life of your barrel... plus the expectations of the shooter such as a f-class / benchrest rifle shooter that might trash a barrel under say 800 rounds OR someone having a good time at the range