"head space" is misunderstood by most people.
Indeed.
<Yes, if headspace is really bad it can cause a problem by means of a case separation but this does not destroy the firearm>
Generally not, but it's by no means a pleasant experience! Thankfully the M98 action handles gas extremely well...
<Enfields are notorious for headspace excess. This causes stretching of the case, but also allowed a dirty rifle to function better>
I'm not an Enfield guy but, off the top of my head, I believe the problem with those isn't so much headspace as it is an oversize chamber to improve functioning under adverse conditions. Same thing with Jap T38s -- they'll headspace just fine on the gage, but the fired cases show a lot of "stretch" at the head. This would ordinarily be indicative of excess headspace, but the problem is that the o/s chamber isn't properly supporting the cartridge case.
<The brass was never used again>
Right! As a result, it was never a problem for the military. And it wasn't a problem for civilian shooters either, until a handloader full-length resized the brass. The cure, of course, is a neck sizing die. Since the body of the case isn't sized, it expands to chamber limits and eventually stops when it can expand no more. Metal fatigue at the case head, caused by expansion and resizing, is eliminated.
<So having excess headspace is not a dangerous thing unless it fails the field gauge. There are several gauges to check this>
A collector need only possess a "no-go" and "field" gage, for the chambering of interest. The "go" gage is primarily used when a barrel is being fitted to an action.
<I have checked headspace on many military firearms and have yet to find one fail the field gauge even on non matching guns>
That's been my experience as well. Perhaps the best (and most easily understood!) treatment of this topic can be found in Hatcher's Notebook. The chapter, oddly enough, is titled "Headspace".
When gage-inspecting headspace, the rifle's bolt should ALWAYS be stripped completely (extractor removed), the chamber and gage should be squeaky clean and dry, and the gage should be examined for imperfections. Use two fingers on the bolt handle, and "feel" the gage as you'd feel the spindle of a micrometer caliper. NEVER force a gage!
Richie