SubMOA,
I see you are from PHX area, check the high power schedule at Rio Salado, South Mountain and Ben Avery, show up at the matches, and ask the high power shooters about their shot out barrels. Most serious competitors pull their barrels when their X count at 600 starts to go down, some even pull barrels at 3000 rounds. These would be AR barrels used across the course matches, 200, 300, and 600.
Hit the mid range and long range shooters as well. Tjese crowd even barrels earlier than across the course shooters.
It would be good to practice on the common type of barrel steel, which mostly are 416 SS used by competitors