Case head seperation is exactly why you should not shoot a rifle with excessive headspace, Hatcher was exactly right and just didn't elaborate the danger of a seperation.
Hatcher also reported on many catastrophic failures of firearms and the causes but metallurgy was still in its infancy during Hatchers time and he was no expert on the subject.
As a general rule, excessive headspace does not cause a catastrophic failure of the firearm unless other factors are also present such as stress fractures, stress risers, poor quality materials used in construction, etc.
Older and surplus rifles contain many of these faults and this is why I will repair one that closes on a no-go gage rather than risk the possibility of injury shooting it as-is.
When a cartridge case fails in the chamber, the gasses normally directed forward tend to jet back jet back towards the shooter.
This will occur even with rifles that have had safety ports incorporated into the design simply because the safety ports cannot be made to a tolerence that will safely vent all the gas without weakening critical points of the design that could lead to catastrophic failure in the course of normal use.
Many, many rifles were not designed to safely deal with rearward directed gasses and as a consequence the shooter receives a very unpleasant faceful of suprises.
If the shooter isn't wearing the all important eye protection, then loss of the dominant eye becomes a real possibility.
5.56Nato and 7.62 NATO can be used with cartridges such as .223 and .308 commercial because the headspace dimensions are so similar between commercial and military that the cartridges can be safely fired in either or chamber.
In most cases the longer Military cartridges will actually load and extract in commercial chambers but it requires quite a bit of force in the loading and unloading cycles.
In semi auto weapons this puts much greater stress forces on the operating parts and can and usually does cause early parts failure.
On manually loaded rifles this isn't so much a result as is frustration and fatigue to the shooter.
This is why the really saavy manufacturers use military dimension chambers in semi auto sporting rifles.
Case stretch still occurs and this is also the reason that saavy manufacturers include a notice recommending that the shooter does not reload the cartridge cases fired in these rifles.
Most especially and specifically, commercial cartridges.
Military cases tend to do much better but many shooters are not educated enough to differentiate and seperate cases used for their reloading purposes.
The stretching of the case weakens it substantially to the point that most commercial cartridge cases can only be reloaded a maximum of once before the possibility that the weakened and reloaded case seperates in the chamber.
