Goes away after cleaning and comes back every time the round count gets past 100 or so. I don't have a hard number, but it is very obvious once you're past 200 rounds.
Whidden Gunworks has a cool set here. Seven gauges are included to indicate headspace from .039″ to .045″. Use these to check existing firearms, when installing prefit barrels, or along with Shim Kits to fine-tune headspace to match your ammunition.