FWIW, if the case and/or projectile are a (very) slight crush fit in the chamber (fore/aft), there will be no excess headspace.
There does, however, need to be something (a chamber step or neck) to crush against.
Close attention does have to be paid to case length, though - since cases usually lengthen with firing.
If the correct AOL is determined, it's fairly easy to make a try gauge from sheet metal for the cases or loaded rounds.
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