headspace tutorial?....

[DonVoigt]

Originally Posted by mrerick

The "Go" and "No-Go" gauges are most useful when you're cutting a chamber. Typically you cut a new chamber to size so that the action closes on a "Go" gauge and will not close on a "No-Go" gauge.

There is also a "Field" gauge, which (by itself) can help ensure that an existing chamber / bolt train combination is safe to fire.

The bolt should never completely close on a "Field" gauge.

Not necessarily, if you read the original post, the bolt barely closed on the no go gage- thus it would have not closed on the field gage.
Actually any resistance to the no go gage means the chamber is between the go and no go gages.

Maybe safe to fire? But still ruined the bolt?

There is more to it than just the gage as told in the "rest of the story". JMHO