I just received an email from a former "colleague" who tells me, as per the "instructions", that "if the gas vent in the barrel is "fouled", it is to be cleared with a "No. 42" drill bit.
I looked up the chart and it tells me that No 42 is 0.0935 inches or, 2.3749 mm.
But, he could not quote the the "last-ditch" oversized hole allowance.
I still cannot find all of my own notebooks, unfortunately.
AustralianL1A1 documentation was in the D250 "decade" (series). The scan of D114 is a scan of an official document ; i.e.., a UK
"Electrical and Mechanical Engineering REGULATION": a whole different family, but still a "rifle" reference. These were not something in my "system" back when I wore the "other" baggy green, down here in the Penal Colonies..
The Brit "numbers" for "adjustment" to the gas vent look 'reasonable" so I will file the excerpt in a sleeve in a ring binder for possible future reference. Perhaps something for a post-port game of "Military Mastermind"?