Jeff,
20/1000" in headspace is quite critical. Typical diff. between go/no go is .004".
That much stretch on a case MIGHT not be a big deal, IF you have your dies set correctly. But, there are a lot of reloaders out there that aren't that sophisticated. They are assembling ammo, not custom reloading!
In this instance, all you have to do, is face .010" off the barrel face, and you're golden.
