BTP,
What would you say to the researches at, for example, The (now Defunct) Small Arms Test Unit at the University of Arkansas at Little Rock, the former director of which said:
Source: http://hybrid.ualr.edu/satu/headspace.htmlWhile not accepted by all, the use of a field gauge to indicate a "safe to fire" firearm WAS used by all the major military forces during the lifetime of a surplus firearm, and was accepted practice. Is your surplus firearm safe if it "won't close on a field gauge"? It was "safe enough" for use by GIs for the M1 rifle, the British for the Lee-Enfield, etc..., and may have come to you unchanged since that use (as far as headspace). YOU determine what you feel is safe for your useage. IF A FIREARM CLOSES ON A FIELD GAUGE, I recommend that you NOT FIRE that arm. According to acceptable practice, that arm is out of spec, and has excessive headspace, and may be dangerous if fired.
Basically, unless you are installing new barrels, you don't need a "go", and even then, a factory cartridge can provide that (some would flame me on that one!)... no go is nice to verify the condition of the firearm (hey, it passed a no go!)... field is likely the more useful for many surplus arms. I have all three for several calibers, and I have never needed or used the "go", but often use the field and no go...
SATU did some apparent study into suppressors that didn't go anywhere, but they did have some sophisticated equipment to measure chamber pressure, and I assume if closing on a NO-GO gauge was dangerous he would be able to report that.
Have you seen any actual incidents of catastrophic structural failures / kBs with firearms that passed the "field gauge" and closed on the "no-go" gauge? All I have been able to find have been related to ridiculous handloads, and the worst I have seen (on milsurps that closed on FIELD gauges) is case separation with no injury to the operator. I have pics of an old enfield that had a paper rubber banded over the action and fired, powder was blown into the paper - but didn't even tear or burn away any of the paper.
I have read some people saying its unsafe, but no substantiated instances of issues that damage the firearm or injure the shooter. If you have any resources confirming these I would be really interested in them.
I'm obviously not going to rush into anything, but I'm also wary of just taking someone's word for it, in either direction.