Recently found a Youtube channel called School of the American Rifle. He's got some pretty specific gauges for measuring everything on the gun.
Video today was on a BCG. He had gauges for bolt tail NO GO and Field. Cam pin hole on the bolt. Bolt face etc, pretty cool stuff.

I did ask in the channel but was wondering where might I be able to buy some of those gauges ?
Not sure if they are all military gauges or customs he had built.

They’re pretty much all USGI armorer gages he has spent many decades and lots of money hunting down and acquiring.

Pin and Ring gages you can order from McMaster-Carr.  That gage he is using to measure the extractor is a firearm specific gage.

Thank you both, had some more time to search after a 14 hour day at work. He does have a ton of stuff and seems pretty passionate about the issue tools.
Just interested in some of the bolt tools and did learn what a ring gauge is. I haven't been in machine shop class for 33 years give or take ?

Thanks again, I'll keep searching and see if there are some equivalents. Did find some promising pics on Vermont Gauge.

Now just need to figure out if it's Ring Gauges for Outside Diameters or Master Ring Gauges...

A lot of the tools are USGI stuff but he does runs of tools from some of his own specs occasionally and people pay exorbitant amounts to get in on that. He is all about perfect specs and while I respect that it is also worthwhile to understand that the AR and many other modern guns were built to run off a set of tolerances due to modern machining and the design itself and will sometimes run completely fine outside of those tolerances as well (which is obviously a good thing, and the tolerances aren't quite the same as Vlad or Abdul did with a file to make AK's run). I did follow and read some of his postings for a while and while I find them very informative it is also common sense to know that it isn't the bible of AR15 wisdom if you have been around and worked on or built rifles yourself.

The info isn't wrong, but there is a sort of cult of personality by a lot of wannabe operators that will shout anyone down that hasn't gauged every single part of their rifle and will praise everything said there on bended knee. It ends up being somewhat of a circle jerk. Not incorrect, but snobbish in many ways. In short, getting gauges or being able to measure parts accurately is good. Telling everyone whose rifle doesn't gauge correctly in every single spec that they will die in the streets is stupid.

Chad is here and has responded to posts many times, his work comes up multiple times per week. His body of work is worthy of respect despite the attitudes and condescension thrown about by followers and occasionally by Chad himself when others question him. Personal opinion: if it runs well despite tolerance stacking, does it matter? Make it a backup and buy a better one.

Good info. I agree but am just interested in some of the bolt tools, like the one he used to find the cam pin hole was stretching in one direction.
I don't have time or the money to buy all those tools but it would be nice to have a few of them to check things after a two or three day class
and see where everything sits. Or if you plan on buying a used gun and checking a few critical areas.

I try to keep major spare parts to a minimum because they invariably end up being a whole new rifle instead of just spare parts.
Guess if you studied the specs, you could have your own gauges made but work doesn't really allow the time for those things.