In the 70's at MacGregor Range (Ft. Bliss) just about every swingin' Delta had all three of these "tools" on him while operating the M2. Sadly, few actually knew the difference .004 (four thousandths of an inch) would make in head space (NO GO is .206 and GO is .202) and what .002 would do to the timing on either the .50 or .30 BMG.
The demo pocket knife almost worked for head space and the P38 was just .002 too much for timing FIRE for both the .50 and .30.
For some strange reason, the real head space gage and pair of timing gages were simply too difficult to use
BTW, the demo knife is not pure stainless and one should not use it for EOD work.
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