I'm looking for the poor man's way to check for excessive headspace in a center-fire rifle. Obviously, the bolt should close without any resistance on brass that has never been fired. My question basically is: How thick of a shim can be placed between the bolt face and the fresh (I would try 5 to 10 of them, to establish an average) brass, before the bolt gets hard to close, or won't close? If I punch out a round piece of aluminum from a can that is slightly smaller in diameter than the rear of the shell, place it behind it, and the bolt will close on it with only slightly more pressure, is that too much headspace? The aluminum is .004" (4 mils) thick. The gun (Savage 7mm rem mag) HAS had some pretty hot loads though it, one in particular that was way too hot, and roughly 500 rounds total through it.