Good video, thanks Doug.
I have the gauges, they are part of my tool collection. I have not had an issue with any of my carbines. Yet that is. I don't remember any issues in full auto over seas. But that has been over forty years ago.
That being said, I'm not saying there is no need to check headspace, we need to error on the side of caution. CMPcarbines have been checked. If you change a barrel, you need to check. Those that reload should take more heed. Check your brass when you trim to length. Also a good point was the use of military verses commercial brass. Not as many reloads with the newer cases. Should add primers to that too. Some are harder then others. Firing pin protrusion, primer flattening, a lot of things to consider.
I think the best thing I saw in the video, don't test it yourself. I think I'll go get my brother in law, his name is Mikey, he'll try anything.