It bewilders me that people who don't know what they are talking about and have not experienced the event they feel compelled to talk about feel so emboldened as to belittle someone who does understand the mechanics of the issue and has actually experienced the event under discussion.
A little less smarmy talky-talky and a little more listening and you could maybe learn something new?
My first experience with a case failure was in a Mauser 98 and the shooter was very lucky not to suffer a serious eye injury. He did end up w a blood blister or hematoma in his eyeball as a result of high pressure gas ejecting stuff into his face. I was standing behind him and got hit in the face with what felt like a pinch of sand. I was wearing glasses, the shooter was not.
My second experience with a case failure was in a AR15 and the high pressure gas mangled the extractor and blew bits of case and extractor out the ejection port. As a lefty I was lucky to not be injured.
Neither event involved the rifle coming to pieces. I had to pound the AR bolt open and replace the extractor. I still have that upper and BCG today and it has worked fine ever since.
Some people here don't seem to understand that the chamber itself is not gas tight. It is the case that provides the gas seal for the chamber and when the case fails, high pressure gas blows out through any route it can and it scours tiny particles of case and sometimes the bolt or other small components in the way with it. Headspace is extremely important to prevent case failure. There is a reason the headspace range specified by SAAMI is only 0.004".
I can fully understand your angst about headspace.
The thing is, you've taken that concern a notch to far IMHO. Not dissing you for it at all, erring on the side of safety can't be put down without good reason and shouldn't be.
A couple of thou of excess headspace isn't going to cause a case failure or a Kaboom.
I've seen Kabooms and case failures in firearms with perfect headspace.
As far as using headspace gauges??? I have a few sets that work for multiple chambers, such as 257Rob/7x57/8x57 and if I'm chambering a rifle for one of those cartridges, all three of which I have the highest regard, I will usually set the headspace up for minimum spec.
Some smiths won't do that. They prefer to set up for something inbetween Min/Max and for good reason. They absolutely hate it when a customer comes back to them and can't chamber a factory round.
The last couple of barrels I chambered, for ''someone else" I didn't have a headspace gauge for and the chambers were a one offs, European designation.
The one fellow had an old reamer for his, in very nice, sharp condition, loading dies and a fired round from his rifle, which had a very long throat and of course, the original barrel.
It was a simple job, rimless case, I used the case which had been fired in his rifle, with a cap of scotch tape over the face to set headspace. The bolt could be closed on the taped cartridge, if you really used substantial force, without the tape the bolt closed positively and smooth, without effort. He was happy, he now had a rifle, chambered for his favorite roung but it's chamber was tight and there wasn't a half inch of freebore, before the bullet engaged the leade.
The other rifle was chambered for a fellow that just had to have a 7x64 S&H.
The difference being he didn't have a barrel but a very nice Shultz and Larson action. He did have a very nice Clymer Reamer and a very decent Schilen barrel, as well as a set of dies and a box of RWS loaded cartridges.
We went through a similar process as above, just with a bit more fiddling, but the same end result.
The bolt could be forced to close on a factory cartridge, with a single strip of scotch tape over the face and would close without effort on the same cartridge without. He did try a couple of other brands of ammo and had no issues with case expansion, unusual stretch etc.
