There's a youtube video of a guy that destroyed an AR barrel in ~850 rounds. The caveat was an M16 lower and non stop mag dumps until the barrel literally began to droop and blew up at the gas block.
The hot high pressure gasses from the cartridge will wear out the chamber of a barrel eventually. The more hot gas you run through the bore and the hotter the barrel is when you run that hot gas through the bore the quicker the throat will be eaten out of the barrel.
Given the cost of ammo, barrels are the cheapest part of the equation. Shoot your rifle until the groups start to open up and then rebarrel.
