I have seen data that lists .0005" as the maximum allowable expansion just ahead of the extractor groove on non belted cases and .0007" on the belt of belted cases.However this only works with new cases as each firing will supposedlywork harden the case slightly.This is taken from a loading manual but I don't recall which one right now.Then again the results can vary if you get a lot of hard or soft brass.I have seen the measurements vary from lot to lot even though the load and resultingvelocity were the same.Most remington and federal loads that I tested expanded .0002" to .0005" when fired in factory rifles,while I have seen weatherby factory loads expand over .002" when fired in weatherby rifles.Some of the new 270wsm and 300wsm factoryloads expanded .001" when fired in factory rifles.These are merely my observations so feel free to either ignore them or to draw whatever conclusions that you see fit.