All rifles increase in headspace as they are used. Typical service life of a ar15 barrel is 20000 to 40000 rounds. There is a gap because of different barrel materials. A higher quality military grade machine gun barrel will last much longer than your typical stainless steel barrel you find on most cheaper budget ar15.
Service life is how long until the gun is not safe to shoot.
Competition shooters replace barrels much sooner since accuracy degrades greatly long before you hit the point a ar15 will close on a field gage
Once you hit the 10000 round mark i would start checking it everytime you service the rifle.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent
Last edited by JonM; 05-25-2013 at 12:54 PM.