Searching for a video of how to...

[JimF4M1s (Deceased)]

Here's an interesting general head spacing video in the Gunsmithing forum which I'm not sure you'll find helpful or not...

Head Spacing (mini lesson) - AGI Gunsmiths

Regards,
Doug

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. CMP carbines 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.

[carwashchris]

First thing first, I think I will check the protrusion of the FP and clean the bolt. I have been using AE & PPU ammo. Have not measured the case length, I'm just assuming they are correct. I'm only getting this problem 2 out of 10 times. I have been able to reload these same rounds and get them to fire on the 2nd or 3rd try.

[imarangemaster]

It may be a problem in the bolt. Carbon builds up in the firing pin chamber and keeps the FP from going forward. Many years ago I had one bolt that did the same. I had to soak in brake cleaner to get the carbon out.