I would think that the NO-GO gauge is the most important but what about the GO gauge?  Should I ever worry about there being too little headspace?  Can I safely tell if the bolt isn't fully closed upon chambering a live round?

If you have a properly built rifle from a mainstream factory you'll never need a headspace gage.  Headspace grows at such a low rate that rifling goes first.

If you buy a rifle from one of the outfits that just assembles like ASA or Rock
River you'll need a min gage most.  Min headspace is more dangerous than over.

You need a 'NO GO' gauge to check for excessive headspace. You need a 'GO' gauge to check for proper headspace when you are using a chamber reamer to ream a chamber in a barrel. You do not blow up guns with minimum headspace. You do increase bolt thrust with excessive headspace. Bolt thrust will cause other problems such as separated case heads, excessive case web expansion, blown primers, etc. I am a professional gunsmith, a retired Marine armorer and a graduate of Yavapai Gunsmithing School. Be careful when you get advice from amateurs such as 'T2'. JarheadGunner.

jarheadgunner,

where in Az. are you ? where do you shoot ? where do you gunsmith ? i live near Tucson & sometymes shoot at the Desert Trails Range.....

Cactus Jack - I reside and practice gunsmithing in Prescott. I shoot in the National Forest northeast of Chino Valley. I once lived in Tucson and frequently shot at the 3 Points range. Let me know at '[email protected]' if I can help you or answer any questions you may have. Thanks. jarheadgunner.