Actually I did check headspace (on all my ex-mil rifles) by using tape spacers on the back of a factory round and seeing how hard it was to close the bolt against. I got shot down by someone once who said it was a stupid way to do it and tape was compressible, so I don't mention it anymore.

As a benchmark, the number of layers of tape corresponded to that on a factory round in my Remington 700 308. Of course this assumes that the factory round has the correct headspace dimensions.