“Moral of the story, never set head space using factory ammo, spend the money for a gage”
You have a head space gage, more of a concern are the cases that chambered after you shimmed the bolt face .007”, meaning you spent the money for a gage and ‘it’ did not work.
Fire forming? Success is not built into fire forming, there is measure before and again after, it is important to know what to do with the difference between the before and after measurements. Had you been measuring the length of the fired cases you would have know the difference between unfired and fired cases was enough to cause the case to separate.
“...spend the money for a gage”, I will assume you are talking about a case length gage like the L. E. Wilson case length gage, to some the Wilson gage is a drop-in gage, others use their thumb nails, others use the sight gage, I prefer the straight edge with the feeler gage, it is possible to use a flat surface, stand the case up then lower the case gage onto the shoulder of the case ‘THEN!’ use a feeler gage to measure from the flat surface to the bottom of the gage.
Again, instruction from Douglas, when installing a barrel, include different methods, not all methods require the use of a gage unless the person understands the case is a gage, the person that understands the case is a gage and is familiar with a reloading press can make gages as long and or short as they choose providing the person installing the barrel knows how to measure the length of the case from the head of the case to its shoulder/datum.